It is rather easy to solve it in Pascal! To my mind. Just take a look at the result: Memory Used 608 K.
http://acm.timus.ru/status.aspx?space=1&pos=789168
I was using an O(N) algorithm, where N stands for "the total number of stack operations" in input file. But I tried to save as much memory as possible. I seem to have managed to do it (:

rafailka.