#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    ios_base::sync_with_stdio(false);

    string str;
    cin >> str;
    int n = str.length();
    int counter = 0;
    for (int i = 0; i < n / 2; i++) {
        if (str[i] != str[n - i - 1]) {
            counter++;
        }
    }
    if (counter != 0) {
        counter -= 1;
    }
    cout << counter;
}