Why was this problem rejudged? I've spent a lot of time writing a solution and at last got AC. It is very disappointing to recieve e-mail with that:
"Wrong Verdict - Accepted
New Verdict - Wrong Answer"
I even don't know why it has happened!!! Tests were changed, checker was rewritten or what?

Several tests were added because old tests didn't check some important features. All tests are correct, please, read problem statement more attentively!

Sorry, I'm stupid! :(((
Of course that was my fault. I got AC after adding one line to my solution.
But it will be very useful to add an explanation to rejudge message on e-mail. For example, "Several tests were added" or "Internal error on server" etc.
Thank you!