Central European Olympiad in Informatics 2026

Welcome!

This is the official website for the 33rd Central European Olympiad in Informatics (CEOI 2026). The CEOI is an annual informatics competition for top secondary school students from Central European countries.

The competition will take place in Ljubljana, Slovenia from TBD to TBD 2026..

Teams from regular participating countries (Croatia, Czech Republic, Germany, Hungary, Poland, Romania, Slovakia, and Slovenia) along with invited guest countries will compete. The competition consists of two days of algorithmic problem-solving, following the International Olympiad in Informatics (IOI) format.

Schedule

X. X. 2026:

Arrival Day & Registration

X. X. 2026:

Opening Ceremony & Practice Contest

X. X. 2026:

Competition Day 1

X. X. 2026:

Excursion & Cultural Day

X. X. 2026:

Competition Day 2

X. X. 2026:

Problem Discussion & Award Ceremony

X. X. 2026:

Departure Day

• Regulations of CEOI
• Contest Rules
• Contest Environment
• Contest System

Regulations of CEOI

Goals

The Central European Olympiad in Informatics (CEOI) aims to motivate secondary school students in Central Europe to:

• get more interested in informatics and information technology in general
• test and prove their competence in solving problems with the help of computers
• exchange knowledge and experience with other students of similar interest and qualification
• establish personal contacts with young people of the Central European region

Additionally, the CEOI may:

• provide training for the students participating in the International Olympiad in Informatics (IOI)
• initiate discussion and cooperation in informatics education in the secondary schools of the Central European countries

Organization of the CEOI

There are eight nine CEOI countries: Croatia, Czech Republic, Germany, Hungary, Poland, Romania, Slovakia, Slovenia and Ukraine.

The CEOI is organized by the Ministry of Education or another appropriate institution of one of the CEOI countries. It is expected that the organization rotates among all CEOI countries at an approximately regular basis. The delegations of all CEOI countries must be invited to each CEOI as regular participants. Moreover, the host country may invite guest countries and a second team from the host country, sharing the same team leader.

The International Committee (IC) of the CEOI consists of the eight nine team leaders and of a representative of the host country who chairs the meetings of the IC. A host who is willing to organize a CEOI in a given year in their country has to announce their intent at least one year before that CEOI (i.e., during the competition days of the previous CEOI). Selection of the next host is made by the IC by a majority vote.

A revision of the CEOI Regulations is adopted by the IC by a 2/3 majority vote.

A new CEOI country can only be adopted by consensus. A country can stop being a CEOI country either by abdicating voluntarily, or by a consensus of all remaining countries.

Delegations and contestant eligibility

A contestant is eligible to compete in the CEOI if and only if they are eligible to compete in the IOI in the same year.

Each contestant must be selected based on their results in national competitions.

A national delegation consists of up to four eligible contestants, a team leader, and at most one deputy leader. Additionally, a delegation can be accompanied by any number of guests.

Participation fees

The delegations of CEOI countries should cover only the cost of their travel to and from the contest site. The host has to cover all reasonable expenses (notably: accommodation, meals, and excursions) of the delegations of CEOI countries during the event. The host can, and usually does, require the delegations of guest countries and the guests who accompany any delegation to pay participation fees.

Scientific Committee

The Scientific Committee (SC) consists of a chairperson and of a number of experts (SC members) from the host country. It becomes active well before the beginning of the Olympiad and has the task of selecting and preparing proposals for competition tasks, including test data and grading schemes. The SC is expected to prepare at least two backup tasks to be used if some of the proposed tasks are rejected by the GA.

General Assembly

The General Assembly (GA) is composed of the team leaders of all participating countries (including guest countries) and of a representative of the host country who chairs the meetings of the GA. GA meetings are held in English.

Before each contest day, the SC presents the GA the proposal for competition tasks and optionally also short descriptions of proposed model solutions and additional details on the tasks. The GA familiarizes themselves with the tasks and then votes on accepting the proposed tasks (by a simple majority). If the proposal is not accepted, the SC presents one or more backup problems and the GA discusses the options and takes votes until some problem set proposal is accepted. After a problem set is accepted, the GA may still suggest minor changes to the problem statements. These changes should improve the clarity of the problem statement without changing the nature of the task. In particular, these changes cannot imply changes in test data or other related materials prepared by the SC.

Competition

At least one month before the competition the host should publish the competition rules for that year and the technical information about hardware and software that will be provided. In particular, the competition rules should define the set of available programming languages, and these should include all languages available at the IOI held in the same year.

The competition consists of two rounds, taking place on different days. In each round the working time is five hours and the contestants are given three problems to solve. Contestants can use the provided programming languages to implement solutions to competition problems. The solutions are evaluated and scored automatically using test data prepared by the SC. During the competition the contestants have the option to submit questions and clarification requests to the SC. All public announcements made by the CEOI authorities to the contestants must also be provided in written form.

The contestants must have the option to use their native language. In particular:

• The team leaders are responsible for translating the official English version of the problem statements into the native language(s) of their contestants.
• The contestants may submit their questions addressed to the SC in their native language.
• The team leaders are responsible for translating such questions into English (and for translating the answer back into the native language, if applicable).

Generally, the contents and the form of the CEOI tasks should be guided by the IOI syllabus.

After the competition, the contestants and team leaders must be given the access to data that will enable them to verify whether their solutions were evaluated correctly. If a team leader does not accept the results of the evaluation and cannot come to an agreement with the SC, the team leader can submit an appeal. The appeal and all relevant data (anonymized if possible) must be presented to the GA by the chair of the SC or the chair of the GA. The GA then takes the final decision on the appeal.

Results and Prizes

About 50% of all contestants (including guest countries and the second team of the host country, if present) should receive medals. The proportion of these gold, silver and bronze medals should be approximately 1:2:3. Given these expectations, the General Assembly will determine the minimum scores for the gold, silver and bronze medals.

Each contestant should receive a certificate of participation. The medals, certificates and other prizes should be given to the contestants at the official closing ceremony.

Contest Rules

These competition rules are derived from those of CEOI 2025, but with quite a few changes in competition details. Relevant changes are highlighted.

Task Types

The tasks are designed to be algorithmic in nature. They may be of the following types:

• Batch – Solutions consist of a single source file of a computer program which reads data from standard input and writes its answer to standard output.
• Communication – Solutions consist of a single source file of a computer program which communicates with a grader program provided by the organizers. The communication interface will be specified in the task statement.
• Output-only – The contestants are given input files and they have to produce correct output files by any means available.

Competition Format

There will be two competition days. On each day contestants will be given three tasks to complete in five hours.

Limits

For batch and communication tasks, the following limits are enforced:

• A contestant can make at most 50 submissions per task.
• Submission size is limited to 50 KiB, unless otherwise stated in the task description.
• Compilation has to run within 10 seconds and within 512 MiB of memory.
• Each task has a given time limit: a limit on the total processor time the solution may consume while solving a single test input. If the solution starts multiple threads, the time limit applies to the sum of their running times.
• Each task has a given memory limit: a limit on the total amount of memory the solution may have allocated at any moment. This limit includes not only the variables but also the executable code, global data, the stack, etc.
• There is no separate stack size limit.

Submitting Solutions

Contestants submit solutions to the contest server via a web-based judging system running on that server.

Solutions for tasks may be submitted at any time during the contest. It is the responsibility of the contestants to submit their solutions to the contest system before the contest is finished. We advise the contestants to reserve enough time before the end of the contest to make sure that all of their solutions are submitted. The contest server shows the official time remaining in the contest.

For tasks that require programs as solutions, the judge will accept C++ source files.

The programs are run on machines similar, but not necessarily identical to the contestants' workstations.

Scoring

Test data for each task will be divided into batches of test cases that correspond to the subtasks defined in the task statement. A single test case is solved correctly if the submitted program produces the correct output within the enforced limits. A subtask is solved correctly if each of the test cases it contains is solved correctly. The individual score for each subtask will be specified in the task statement.

If a contestant submits more than one solution for the same task, the final score for each subtask will be the maximum score of this subtask across all submissions. The final score for each task will be the sum of scores for its subtasks. For example, consider a contestant who made two submissions on a task that contains two subtasks. The first submitted solution got 30 points for the first subtask and 10 points for the second subtask. The second solution got 0 points for the first subtask and 40 points for the second subtask. Hence, the final score for this task will be 70.

Each submission is always tested on all sample test cases. The results of these tests have no influence on the scores. In particular, it is possible to fail a sample test case and still gain a non-zero score for the task.

Scoring procedures for a task that deviates from the above will be specified in the task description.

Feedback

For each submission, the judging system will provide as feedback the verdict and score for each subtask.

If a subtask is not solved, then the judging system will provide feedback for the first test case which received the lowest score on that subtask. The feedback will include the test case number and one of the following reasons:

• Partially correct: The submission was executed within all limits and produced a partially correct solution for the test case.
• Not correct: The submission was executed within all limits and produced an incorrect solution for the test case.
• Timed out: The submission did not finish within the time limit.
• Killed by a signal: The evaluation terminated after receiving a fatal signal. This might be caused by exceeding the memory limit.
• Non-zero exit code: The submission terminated its execution with a non-zero exit status.

Inputs are ordered the same way in all the runs. No information on the actual data, number of passed test cases, program output, or any other execution details will be given to the contestant.

A correctly solved subtask will receive a Correct verdict.

If compilation of a submission fails, the contestant will receive the compiler output.

Feedback provided for a task that deviates from the above will be specified in the task description.

There is a small chance that the verdict will change later:

• If there is an error found in the test data, the Scientific Committee may fix it and re-evaluate all submissions.
• Submissions can be re-evaluated on the same test data at any time. This might affect non-deterministic solutions or solutions running very close to the time or memory limit.

Clarification Requests

During the competition, contestants may use the judging system to submit clarification requests. Contestants may use English or their native language. Delegation leaders are responsible for translations between the native language and English.

Task-related questions must be phrased as positive yes/no questions. These questions will be answered with one of the following:

• YES
• NO
• ANSWERED IN TASK DESCRIPTION (EXPLICITLY OR IMPLICITLY): The task description contains sufficient information. The contestant should read it again carefully.
• INVALID QUESTION: The question is not phrased so that a yes/no answer would be meaningful. The contestant is encouraged to rephrase the question.
• NO COMMENT: The contestant is asking for information that the Scientific Committee cannot give.

The Scientific Committee may choose to provide additional information.

Technical and contest-related questions and comments may be phrased arbitrarily and the Scientific/Technical Committee will answer them appropriately.

Announcements

The Scientific Committee may need to make an announcement during the competition. These announcements will be made in English and they will be published on the judging system. If a contestant cannot understand the English announcement, they can send a clarification request asking for a translation.

Fair Play

In order to ensure fair competition, submitted programs are not allowed to:

• execute other programs;
• access the network;
• read or write files not described in the task description;
• attempt to subvert the security of the grader.

During the contest, contestants are not allowed to:

• access any workstation other than the one assigned to them;
• access the network for anything other than communicating with the judging system;
• attempt to gain access to user accounts different from their own;
• attempt to overload the judging system or attack its security in any way;
• reverse engineer the test data in order to solve the problems in highly test-data-dependent manner. One example of such behavior is using the feedback system to extract the test data and the applying this knowledge to build solutions adapted to the specific test cases. This behaviour would be considered cheating only if a submitted solution would solve significantly fewer test cases correctly if the test data were replaced by an equivalent set of test cases (e.g., one generated with a different random seed);
• communicate with persons other than CEOI staff or onsite proctors;
• reveal their passwords;
• intentionally damage or endanger any part of the competition environment;
• reboot their workstation;
• access their workstation outside of the provided virtual machine;
• use any printed and/or electronic materials that are not explicitly allowed.

All Fair Play limits do apply during the practice session as well. Violation of these rules may be grounds for disqualification.

Delegation leaders must protect confidentiality of tasks. Between the moment the tasks are presented to the General Assembly and the end of the corresponding competition day, contestants must not communicate with anyone who knows the tasks except for the usual communication with CEOI staff. During that time, sharing task-related information with anybody outside the General Assembly requires an explicit approval from the Scientific Committee.

Competition Supplies

During the contest days, the onsite proctors will provide:

• pens and blank paper;
• snacks and drinks.

During the practice session and analysis session, contestants may bring anything they like. During the contest, contestants may only bring the following items:

• writing utensils;
• simple wristwatches;
• keyboards and mice (with no wireless communication and no programmable functions whose configuration is retained when unplugged);
• small mascots;
• English dictionaries;
• clothing and reasonable jewelry;
• medicine and medical equipment;
• earplugs and earmuffs.

During the onsite practice session, all keyboards, mice, mascots, and dictionaries must be submitted to the onsite proctors for approval before they can be installed and used. After the practice session, and again after the analysis session after the first competition day, these items must remain on the contestant’s desk. After the second competition day, the contestant is responsible for collecting all their belongings.

Any attempts to bring any other items unlisted above into the competition rooms are considered cheating. In particular, the following items are strictly prohibited in the competitions:

• any computing equipment (calculators, laptops, tablets, smart watches, …);
• any books, manuals, written or printed materials;
• data storage media (USB drives, flash cards, …);
• communication devices (mobile phones, radios, Bluetooth-enabled devices, …).

Appeal Process

During the analysis session after a contest day, the secret test data will be made available to the contestants and delegation leaders. Contestants and team leaders may use the contestant workstations to verify that the grading is correct.

A team leader must notify the Scientific Committee about any appeals before the end of an analysis session, and then submit the full text of the appeal in the time specified by the Scientific Committee.

Every appeal will be reviewed by the Scientific Committee and the team leader will be notified about the committee's decision. All appeals and their resolutions will be summarized at a General Assembly meeting and approved by the GA.

In the event that a mistake is discovered in the grading of a task, the mistake will be corrected and the submissions of all contestants will be re-graded and re-scored, whether or not the scoring of that particular submission has been appealed. Note that re-scoring may result in a higher or lower score for any contestant.

Contest Environment

The software environment of CEOI 2026 consists of Ubuntu 24.04 LTS with the Xfce desktop environment. The following packages are provided:

• Compiler: GCC 13.3 in C++20 mode
• Interpreters: Python 3.12 (for local testing only; solutions must be submitted in C++)
• Text editors and IDEs: Vim, Geany, Kate, Emacs, Visual Studio Code, PyCharm
• Debuggers: gdb, valgrind
• Web browsers: Firefox

Contest System

CEOI 2026 uses the following software:

• Slovenian contest management system - https://contest.ceoi2026.acm.si/.
• The task translation system from the IOI.

Contest

The contest system and live results will be accessed at https://contest.ceoi2026.acm.si/ (PLACEHOLDER).

Contest data (will be available after the event):

• Contest tasks: [Tasks will be uploaded here]
• Public scoreboard: [Link to Public Scoreboard]
• Test data and solutions: [Link to zip file]
• Presentation of solutions: [Link to PDF]

Contest results (Scoreboard Placeholder):

Venue

The CEOI 2026 competition will be held in Ljubljana, Slovenia. The likely competition venue is the **Faculty of Computer and Information Science (FRI)** at the University of Ljubljana, which has modern facilities suitable for the Olympiad.

Official registration, social events, and opening/closing ceremonies may take place at other prominent Ljubljana locations, such as Cankarjev Dom.

Organizers

The Central European Olympiad in Informatics 2026 is the result of efforts of many people.

Regional contest director

• Andrej Brodnik

Organizing Committee

• Andrej Brodnik (chair)
• TBD

Scientific Committee

• Tomaž Hočevar (chair)
• Janez Brank
• Vid Kocijan
• Jure Slak
• TBD

Technical Committee

• Jan Berčič (chair)
• Gašper Fele Žorž
• Jure Slak

Staff

• TBD

Contact

For general inquiries about CEOI 2026, please contact the organizing committee at:

ceoi@acm.si (PLACEHOLDER)