Most of the time that sounds like a problems with I/O. Please notice, that in task you're trying to submit, there are input and output files and not stdin/stdout. So, when it gets to cin, it just idles, awaiting that someone comes to the test machine and enters data. Which probably isn't going to happen. Hope that helps!

The problem has input file input.txt and output file output.txt (you can see this in the top of the problem statement). This is not typical for Codeforces, but you need to uncomment your freopen code (with input.txt and output.txt as I/O, of course).