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;

typedef long long ll;
#define rep(i,n) for( ll (i)=0; (i)<(n); ++(i) )
#define rpi(i,n) for( int (i)=0; (i)<(n); ++(i) )
#define rpv(d) for(auto& v:d)
#if __cplusplus < 201703L
  std::ostream& co_(){ return std::cout << std::endl; }
  std::istream& cn_(){ return std::cin; }
  template<class Head, class... Args>
  std::ostream& co_( Head&& head, Args&&... args ){ std::cout << head; return co_(std::forward<Args>(args)...); }
  template<class Head, class... Args>
  std::istream& cn_( Head&& head, Args&&... args ){ std::cin >> head; return cn_(std::forward<Args>(args)...); }
#else
  template<class... Args>
  std::ostream& co_( Args... args ){ return std::cout << ... << args << std::endl; }
  template<class... Args>
  std::istream& cn_( Args... args ){ return std::cin >> ... >> args; }
#endif
#define co(...) co_(__VA_ARGS__);
#define cn(...) cn_(__VA_ARGS__);
#define all(x) (x).begin(), (x).end()
#define rgt(x,i) (x).begin(), (x).begin()+(i)

int main(){
  string s;cn(s)
  int ans = 0;
  rpi(i,s.size()/2){
    if ( s[i] != s[s.size()-1-i] )++ans;
  }
  co(ans)
}