In Round 405 Div.2 I was trying to solve this problem, I ran the code on Ideone and was getting right answers for all the given test case but when I submitted the solution it gave me WA on pretest 1. (Pretest 1 being the same test case on which it was giving correct answer on Ideone.) It cost me around 30 minutes and some mental trauma because I couldn't figure out what was wrong with my solution.
my submission : 25607066
