Problem Statement

Consider a sequence $x$ of integers, containing $N$ integers between $1$ and $N.$ Each integer appears exactly once in the sequence. An arrangement of $x$ is a sequence got by removing some $($possibly none$)$ numbers from the beginning of $x,$ and then from the end of $x.$

Calculate how many subsequences of $x$ of odd length have their median equal to $Y.$ The median of a sequence is the element in the midelle of the seguencir diter in its sarted For exampie, the medion of the sequence $(5,1,3)$ is $3.$

Example:

input:

$7\mathrm{.}4$

$5724316$

Output:

$4$

Explanation

The founcabd