Palindrome

Given string. In one operation you can swap any two letters. Find minimum number of operations needed in order to receive palindrome or -1 if it is impossible.

Input

First line contains one string s (1 ≤ |s| ≤ 1000). Given string is not empty and only contains small latin letters.

Output

Print the minimum number of operations needed in order to receive palindrome or -1 if it is impossible.

Examples