Ok, so I solved this problem: http://mirror.codeforces.com/contest/91/problem/A. The interesting thing is that I submitted 2 buggy solutions before: 27178776 and 27178719. They are exactly the same, but one is compiled on C++11 and the other on C++14. My question is: why is there a difference? Does it have to do with the way C++11 and C++14 handles the way a vector works when you access the vector.size()th element (which doesn't exist)?