I solve this problem with C++ first and got WA#6, but I can't find where is my problem, so I rewrite it with C# with the same solution, but to my surprise, this time I got AC.
And even till now I don't know what are the differences between my two lovely code.
Any idea?
//Sorry for my poor English

Idea - those two solutions are not the same really.
What else do you expect w/o any code?
BTW, you can write random generator of big tests and run and compare outputs of two solutions till you'll find a difference.