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 PyPy3 (2.4.0) (judge verdict: Runtime Error)

#include "bits/stdc++.h"5 7 5
using namespace std;
typedef long long int ll;
typedef vector<ll> vl;
typedef pair<ll, ll> PP;
#define rep(i,n) for(ll i = 0; i < ll(n); i++)
#define all(v) v.begin() , v.end()
#define inputv(v,n) rep(i,n){\
    ll x;\
    cin>>x;\
    v.push_back(x);\
    }
const ll INF = 999999999999999;
const ll MOD = 1000000007;
ll a, b, c, d, e, f, p, t, x, y, z, q, m, n, r, h, k, w, l, ans = 0;
int main() {
	string S;
	cin >> S;
	n = S.length() / 2;
	rep(i, n) {
		if (S[i] != S[S.length() - 1 - i])ans++;
	}

	cout << ans << endl;
}