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 task "A"
#define ALL(v) (v).begin(), (v).end()
#define rep(i, l, r) for (int i = (l); i <= (r); ++i)
#define Rep(i, r, l) for (int i = (r); i >= (l); --i)
#define DEBUG(X) { cerr << #X << " = " << (X) << '\n'; }
#define PR(A, n) { cerr << #A << " = "; FOR(_, 1, n) cerr << A[_] << ' '; cerr << '\n'; }
#define sz(x) ((int)(x).size())
#define pb push_back
#define F first
#define S second
#define by(x) [](const auto& a, const auto& b) { return a.x < b.x; } // sort(arr, arr + N, by(a));
#define next ackjalscjaowjico
#define prev ajcsoua0wucckjsl
#define y1 alkscj9u20cjeijc
#define left lajcljascjljl
#define right aucouasocjolkjl
#define y0 u9cqu3jioajc

using ll = long long;
using ld = long double;
using ull = unsigned long long;

using namespace std;

typedef pair<int,int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<ll> vl;
string s;
int ans = 0;
int main()
{
	//freopen(task".in","r",stdin);
	//freopen(task".out","w",stdout);
	ios_base::sync_with_stdio(false);cin.tie(nullptr);
	cin >> s;
	int n = sz(s);
	s = '0' + s;
	rep(i, 1, n / 2) if (s[i] != s[n - i + 1]) ans++;
	cout << ans;
}