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));
$len = strlen($str);
$hag = 0;
$herflen = ceil($len / 2);
for ($i = 0;$i < $herflen;++$i) {
    $front = substr($str,$i,1);
    $back = substr($str,$len - ($i + 1),1);
    if ($front !== $back) {
        ++$hag;
    }
}
echo $hag.PHP_EOL;
?>