Problem:
Score : 200 points

Problem Statement

Takahashi loves palindromes. Non-palindromic strings are unacceptable to him. Each time he hugs a string, he can change one of its characters to any character of his choice.

Given is a string S. Find the minimum number of hugs needed to make S palindromic.

Constraints

S is a string consisting of lowercase English letters.

The length of S is between 1 and 100 (inclusive).

Input

Input is given from Standard Input in the following format:

S

Output

Print the minimum number of hugs needed to make S palindromic.

Sample Input 1

redcoder

Sample Output 1

1

For example, we can change the fourth character to o and get a palindrome redooder.

Sample Input 2

vvvvvv

Sample Output 2

0

We might need no hugs at all.

Sample Input 3

abcdabc

Sample Output 3

2

Solution in PHP (5.6.30) (judge verdict: Accepted)

<?php
    $str = trim(fgets(STDIN));
    $length = floor(strlen($str) / 2);
    $def = 0;
    for($i=0; $i<$length; $i++){
        $a = substr($str, $i , 1);
        $b = substr($str, -($i+1) , 1);
        if($a != $b){
            $def++;
        }
    }
    echo $def;
?>