Problem Link: https://mirror.codeforces.com/contest/1809/problem/B

(Recent Edu Round Problem B)

Please watch these submissions for Problem B from my id:

https://mirror.codeforces.com/contest/1809/submission/198866759 : Says TLE on Test 1

https://mirror.codeforces.com/contest/1809/submission/198864293 : Says WA on Test 2

And now watch the same solution submitted by my friend after contest:

https://mirror.codeforces.com/contest/1809/submission/198867203 : SAYS AC !

Please explain the happening !

also all I tried to hack a cout<<sqrt(n-1) solution and I failed, so please find the bug.