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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program palindrome_philia
    implicit none
    character(100):: s
    integer(4):: i, ans, s_len

    read*, s
    ans = 0
    s_len = len_trim(s)
    
    do i = 1, s_len/2
        if (s(i:i) /= s(s_len-i+1:s_len-i+1)) ans = ans+1
    end do

    print*, ans
end program palindrome_philia