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
    $line = trim(fgets(STDIN));
    $arr1 = str_split($line);
    $arr2 = $arr1;
    krsort($arr1);
    foreach ($arr1 as $key => $val) {
        $arr3[] = $val;
    }
    $cnt = 0;
    for ($i=0;$i<count($arr1);$i++){
        if($arr2[$i] != $arr3[$i]){
            $cnt++;
        }
    }
    echo $cnt/2;