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, n) for (int i=0; i<(int)(n); i++)
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
template<class T> inline bool chmin(T& a, T b){if (a>b){a = b; return true;}return false;}
template<class T> inline bool chmax(T& a, T b){if (a<b){a = b; return true;}return false;}
/*
void chmin(ll a, ll b){if (a>b){a = b; return true;}return false;}
void chmax(ll a, ll b){if (a<b){a = b; return true;}return false;}
*/

const ll MOD = 1000000007;
const ll INF = 9999999999;

int main() {
  string s; cin >>s;
  int a,b;
  if (s.size() % 2 == 0){
    b = s.size()/2; a = b-1;
    // 0 1 2 3: 4
  }else{
    a = s.size()/2-1; b = a+2;
    // 0 1 2 3 4: 5
  }
  
  int ans = 0;
  for (int i=0; i<=a; i++){
    if (s.at(i) != s.at(s.size()-1-i)){
      ans++;
    }
  }

  cout <<ans <<endl;
}