I am not able to solve problem "once upon a time" from this(http://codeforces.net/gym/100963/attachments) set . I tried extended euclidean algorithm. Can anyone provide the solution (in form of code or editorial) for this problem Or help me debug my code (http://codeforces.net/gym/100963/attachments) .

I am getting WA in Spoj Problem ,Build the fence . Link to the problem : https://www.spoj.com/problems/BSHEEP/ Link to my code : https://ideone.com/NpcblK . Can anyone help me to find the error or give any counter test case. I used graham scan algorithm to make my code efficient.

How to calculate (a power b) mod p correctly if b is exceeding long long integer limit in c++.