875. Minimum Moves to Make Palindrome

0

Hard

Given a string s consisting only of lowercase English letters, determine the minimum number of moves needed to make s a palindrome. In one move, you can select any two adjacent characters of s and swap them. Note that the input will be generated such that s can always be converted to a palindrome.

Input Format

The first line contains a single integer N, the length of the string. The next line contains the string s.

Output Format

An integer representing the minimum number of moves to make the string a palindrome.

Example

Input

4
aabb

Output

2

Constraints

1 <= N <= 2*10^3

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