Problem Description

Given a permutation $a_1, \dots, a_n$ of $1 \sim n$ with length $n$, find how many subarrays of odd length have median $B$.

• Definition of subarray: the remaining sequence after deleting some numbers from the beginning (possibly none) and some numbers from the end (possibly none) of this permutation.

• Definition of median: after sorting a sequence in increasing order, the number that is in the middle.

Input Format

The first line contains two integers $n, B$.

The second line contains $n$ integers, a permutation of $1 \sim n$.

Output Format

Output the number of odd-length subarrays whose median is $B$.

5 4
1 2 3 4 5

2

6 3
1 2 4 5 6 3

1

7 4
5 7 2 4 3 1 6

4

Hint

Explanation for Sample $3$

All possible cases are: 4 7 2 4 5 7 2 4 3 5 7 2 4 3 1 6.

Constraints

For $100\%$ of the testdata, it is guaranteed that $1 \le n \le 10^5$, $1 \le B \le n$.

Notes

This problem is translated from COCI2007-2008 CONTEST #1 T5 SREDNJI

Translated by ChatGPT 5