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;
using lint = long long;

// macros
#ifndef STOP_DEBUG
#define debug(...)\
    do { cerr << boolalpha << "[" << #__VA_ARGS__ << "]:";\
    debug_cerr(__VA_ARGS__); cerr << noboolalpha; } while (0)
#else
#define debug(...)
#endif

// functions
void debug_cerr(){ cerr << '\n'; }
template<class Head, class... Tail>
void debug_cerr(Head head, Tail... tail){
  cerr << ' ' << head;
  debug_cerr(tail...);
}
void chmax(lint &a, lint b) { if (a < b) a = b; }
void chmin(lint &a, lint b) { if (a > b) a = b; }

// cin/cout setup
struct IoSetup{
    IoSetup(){
      ios::sync_with_stdio(false);
      cin.tie(nullptr);
      cout << fixed << setprecision(20);
    }
} iosetup;


int main() {
  string str1;
  cin >> str1;
  int sum = 0;
  for (int i = 0; i < str1.size() / 2; ++i) {
    if (str1.at(i) != str1.at(str1.size()-i-1)) {
      sum++;
    }
  }
  
  cout << sum << '\n';
}