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 (Clang 3.8.0) (judge verdict: Accepted)

#include <iostream>
#include <stdio.h>
#include <vector>
#include <algorithm>
#include <cmath>
#define rep(i,cc,n) for(int i=cc;i<=n;++i)
#define drep(i,cc,n) for(int i=cc;i>=n;--i)
typedef long long ll;
using namespace std;
int main(){
    string s;
    cin>>s;
    int n = s.size();
    int ans=0;
    rep(i,0,n/2-1){
        if(s[i]!=s[n-1-i]) ans++;
    }
    cout<<ans<<endl;
    return 0;
}