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)

# ABC147b


def main():
    import sys
    input = sys.stdin.readline
    sys.setrecursionlimit(10**6)

    # map(int,input().split())
    s = input()[:-1]
    ans = 0
    for i in range(len(s) // 2):
        if s[i] != s[-i-1]:
            #print(s[i], s[-i-1])
            ans += 1
    print(ans)


if __name__ == '__main__':
    main()