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: Accepted)

import math


def inputIntList():
    return [int(s) for s in input().split()]


def inputInt():
    return int(input())


def main():
    S = input()
    cnt = 0
    for s, r in zip(S[: int(len(S) / 2) + 1], S[: int(len(S) / 2) - 1 : -1]):
        # print(s, r)
        if s != r:
            cnt += 1

    return cnt


if __name__ == "__main__":
    print(main())