Merry Christmas, Codeforces! 🎄 🎄 🎄

We are glad to invite you to take part in Good Bye 2025, which will start on Dec/27/2025 17:35 (Moscow time). You will be given 9 problems and 3 hours to solve them. At least one problem will be interactive, so please make sure to read the guide for interactive problems before the contest. This round is open and rated for everyone.

Problems are authored by conqueror_of_tourist, twosquares, and YuukiS.

We would like to thank:

• Error_Yuan for his wonderful coordination.
• Alexdat2000 for Russian translation.
• Geothermal, Um_nik, and Dominater069 for nutella testing.
• __baozii__ for remaining an IGM during testing (unlike me).
• BucketPotato, kevinyang, golomb, xiaowuc1, apgpsoop, and 4fecta for red testing.
• kevin, Auchenai01, and _odium for testing and being an IM at some point in their lives (unlike conqueror_of_tourist).
• sszcdjr, fishy15, fwfjs, applepi216, beaaaan, zhed, Julto, and ow3nL for yellow testing.
• ToxicPie9, shcal, Gilwall, biximo, RTE, and aggrovector for purple testing.
• djrfrn, Leaves333, mtand872, chromate00, and mathtsai for blue testing.
• laze, LetianPie, RockingMat, and pranp_24 for cyan testing.
• waterbottledude for making sure we get every color (maybe you can test after the contest!!).
• Milmon and elituni for gray testing.
• jaguar713 for truly making sure we get every color (and drawing multiple diagrams).
• MikeMirzayanov and KAN for the great Codeforces and Polygon platforms.

• You

  for participating in this round.

Update 1: The score distribution is as follows

⛄ We hope you'll enjoy the problems! ⛄

Update 2: Hacks will be disabled on problems A-E.

Update 3: Editorial

Update 4: Congratulations to the winners!

1. jiangly
2. Benq
3. Kevin114514
4. VivaciousAubergine
5. ecnerwala
6. StarSilk
7. Radewoosh
8. Ormlis
9. ksun48
10. BreakPlay

We sincerely hope you enjoyed a nonnegative number of problems on the round. We hope you have a Happy New Year (both on CF and irl... maybe go touch some grass for the first time this year)!