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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<ll, ll> pll;

#define m0(x) memset(x, 0, sizeof(x))
#define all(x) x.begin(), x.end()
#define rep(i, n) for(int i = 0; i < (n); i++)
#define asort(x) sort(all(x));
#define dsort(x, t) sort(x.begin(), x.end(), greater<t>());
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());
#define MINS(m, s) m.insert(make_pair(s, 1));
#define MFIN(m, s) m.find(s) != m.end()
#define INF (1 << 29)
const int mod = 1000000007;

int main() {
    string s;
    cin >> s;

    int cnt = 0;
    int len = s.length();
    for(int i = 0; i < len / 2; i++) {
        if(s[i] != s[len - i - 1]) {
            cnt++;
        }
    }
    cout << cnt << endl;
    return 0;
}