Hello, Codeforces!

We are glad to invite you to take part in Hello 2026, which will start on Wednesday, January 7, 2026 at 22:35UTC+8. 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 wangmarui, Gold14526, Hoks_, Neil_Qian, Network_Error, jiazhichen844 and xvchongyv.

We would like to thank:

• Proof_by_QED for his wonderful coordination.
• Alexdat2000 for Russian translation.
• Geothermal, StarSilk, and Dominater069 for nutella testing.
• nldr, max0810, A_G, _istil, ian_HLX, nifeshe, paulzrm, sammyuri and Intellegent for red testing.
• Genius_Star_rgw, incra, lkrqwq, LaDeX, pichax, shiny_shine, efishel, Edeeva, Register, omsincoconut, Watersphere, Lilypad, Caylex and waauto 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.