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>
#define rep(i,cc,n) for(int i=cc;i<=n;++i)
#define drep(i,cc,n) for(int i=cc;i>=n;--i)
#define sz(s) (int)(s.size())
#define vecprint(v) rep(i,0,v.size()-1)cout << v[i] << " ";cout << endl;
using namespace std;
const int mod=1000000007;
typedef long long ll;
typedef pair<int,int> P;

int main(){
    string s;
    cin >> s;
    int n = sz(s);
    string rs = s;
    reverse(rs.begin(),rs.end());
    int ans = 0;
    rep(i,0,n/2-1){
        if(s[i]!=rs[i])++ans;
    }

    cout << ans << endl;
//  printf("%.10f\n",ans);

    return 0;
}