\(4^{th}\) round, January \(19^{th}\), 2013

Mirko's latest homework assignment is writing an essay. However, he finds writing essays so boring
that, after working for two hours, he realized that all he has written are N long words consisting
entirely of letters A and B. Having accepted that he will never finish the essay in time, poor Mirko has
decided to at least have some fun with it by counting nice words.
Mirko is connecting pairs of identical letters (A with A, B with B) by drawing arches above the word.
A given word is nice if each letter can be connected to exactly one other letter in such a way that no
two arches intersect. Help Mirko count how many words are nice.

The first line of input contains the positive integer N (\(1 \le N \le 100\)), the number of words written
down by Mirko.
Each of the following N lines contains a single word consisting of letters A and B, with length between
2 and 100 000, inclusive. The sum of lengths of all words doesn't exceed 1 000 000.

The first and only line of output must contain the number of nice words.

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출처 COCI 2012/2013 Contest 4