Trick or participate, Codeforces?

We are glad to invite you to our Halloween round, Codeforces Round 1131 (Div. 3), which will start on Oct/31/2026 17:35 (Moscow time).

The problems were authored by wuhudsm, and prepared by wuhudsm and wakanda-forever

You will be given 7 problems and 135 minutes to solve.

The round will be hosted by rules of educational rounds (extended ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of open hacks. After open hacks all accepted solutions will be rejudged on successful hacks.

Note that the penalty for each wrong submission in this round is 10 minutes. Also, note the rule restricting AI use!!! If you are caught using AI in an unorthodox manner, bad things will happen to you. We will be watching you all...

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participant of the third division, you must:

• take part in at least five rated rounds (and solve at least one problem in each of them)
• do not have a rating of 1900 or higher at any moment in time.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you (unless you register unrated).

I would like to thank:

• cry for coordinating the round;
• __baozii__ for GM testing;
• Edu175, and omsincoconut for M testing;
• Edeeva, WorldWarV, and yse for CM testing;
• Vladosiya, DivinePunishment, CatsAreCool, Bal_Krishna04, Eikyu,simplelife, expertaq, chromate00, and nik_exists for Expert testing;
• Saidul_1, and linearspace for Specialist testing;
• MikeMirzayanov for the great Codeforces and Polygon platforms;
• And at last but not least, You for participating in the round!