Srednji

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 $B$.

In Sample Input 3, the four subsequences of $A$ with median $4$ are $(4)$, $(7, 2, 4)$, $(5, 7, 2, 4, 3)$ and $(5, 7, 2, 4, 3, 1, 6)$.

Sample Input 1 | Sample Output 1 |
---|---|

5 4 1 2 3 4 5 |
2 |

Sample Input 2 | Sample Output 2 |
---|---|

6 3 1 2 4 5 6 3 |
1 |

Sample Input 3 | Sample Output 3 |
---|---|

7 4 5 7 2 4 3 1 6 |
4 |