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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php
list($S)=sscanf(trim(fgets(STDIN)),"%s");
$h = (int)(strlen($S)/2);
$a = substr($S,0,$h);
$b = strrev(substr($S,$h*-1));
$cnt = 0;
for($i=0;$i<$h;$i++){
    if($a[$i] != $b[$i]){
        $cnt++;
    }
}
printf($cnt);