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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;

#define rep(i,n) for (int i = 0; i< (n); ++i)
#define vvec(m,n) vector<vector<int>> (int(m), vector<int>(n))
#define ALL(a) (a).begin(), (a).end()

using ll = long long;

int main(){
    string s;
    cin >> s;
    int ans = 0;
    rep(i,s.size()/2){
        if(s.at(i) != s.at(s.size()-i-1)){
            ans++;
        }
    }
    cout << ans << endl;
}