I think they are cheated https://mirror.codeforces.com/contest/1850/submission/214920611; https://mirror.codeforces.com/contest/1850/submission/214917143; https://mirror.codeforces.com/contest/1850/submission/214868771; https://mirror.codeforces.com/contest/1850/submission/214868771 and more SlavicG