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 Python (3.4.3) (judge verdict: Wrong Answer)

s = (input())

n = len(s)
if n % 2 == 0:
    s1 = [x for x in sorted(s[0:(int(n/2))], reverse = False)]
    s2 = [x for x in sorted(s[(int(n/2)):n], reverse = True)]
    num = 0
    for i in range(int(n/2)):
        if s1[i] != s2[i]:
            num += 1
    print(num)
else:
    s1 = [x for x in sorted(s[0:(int((n-1)/2))], reverse = False)]
    s2 = [x for x in sorted(s[(int((n+1)/2)):n], reverse = True)]
    num = 0
    for i in range(int(n/2)):
        if s1[i] != s2[i]:
            num += 1
    print(num)