Competitions

# KBTU OPEN 2014 Spring

# 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.

Input example #1

abab

Output example #1

1

Input example #2

abc

Output example #2

-1