see this: https://mirror.codeforces.com/problemset/problem/1285/B

i understood the problem but could not identify how to solve it.. i read the editorial btw don't understood.. please give me a proper idea.. :(

see this link: https://mirror.codeforces.com/contest/1284/submission/68190516

ios_base :: sync_with_stdio(false); cin.tie(NULL);

when remove this two line it got ac.. but before wa.. why and how??