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

fscanf(STDIN, "%s", $s);

$len = strlen($s);

$first = substr($s, 0, floor($len / 2));
$last = substr($s, ceil($len / 2));
$last_rev = strrev($last);

$first_arr = str_split($first);
$last_arr = str_split($last_rev);

$count = 0;
foreach ($first_arr as $i => $first_char) {
    if ($first_char !== $last_arr[$i]) {
        ++$count;
    }
}

echo $count;