Consider a sequence \(A\) of integers, containing \(N\) integers between \(1\) and \(N\). Each integer appears exactly once in the sequence.

A subsequence of \(A\) is a sequence obtained by removing some (possibly none) numbers from the beginning of \(A\), and then from the end of \(A\).

Calculate how many different subsequences of \(A\) of odd length have their median equal to \(B\). The median of a sequence is the element in the middle of the sequence after it is sorted. For example, the median of the sequence \(\{5, 1, 3\}\) is \(3\).

The first line contains two integers, \(N\) (\(1 \le N \le 100\,000\)) and \(B\) (\(1 \le B \le N\)).

The second line contains \(N\) integers separated by spaces, the elements of sequence \(A\).

Output the number of subsequences of \(A\) whose median is \(B\).

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출처 COCI 2007/2008 Contest 1