SREDNJI

문제

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.

입력

The first line contains two integers, N (1 ≤ N ≤ 100000) and B (1 ≤ B ≤ N). 

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

출력

Output the number of subsequences of A whose median is B. 

힌트

In the third example, the four subsequences of A with median 4 are {4}, {7, 2, 4}, {5, 7, 2, 4, 3} and {5, 7, 2, 4, 3, 1, 6}.

7 4
5 7 2 4 3 1 6

4

6 3
1 2 4 5 6 3

1

5 4
1 2 3 4 5

2