Welcome to the Codeforces Beta Round #90! I (Sergey Sukhov) and Alexander Ignatyev (dudkamaster) have prepared for you today's contest. We thank Artem Rakhov (RAD) for help and useful hints, Mariya Belova (Delinur) for translation of statements, as well as Michael Mirzayanov (MikeMirzayanov) for opportunity to conduct this round.
Good luck and high rating!
UPD. Unfortunately the mistake was found in author's solution of problem B, therefore this round will be unrated. We present our apologies.
UPD2. Analysis of problems A-D is published.