#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <string>

using namespace std;

int l, t;
string s;

int main() {
    cin >> s;
    l = s.length();
    t = 0;
    for (int i = 0; i < l / 2; i++) {
        if (s[i] == s[l-i-1]) {
            continue;
        } else if (s[i] != s[l-i-1] && s[i+1] != s[l-i-2]) {
            t++;
            s[i] = s[l-i-1];
            s[i+1] = s[l-i-2];
        } else if (s[i] != s[l-i-1] && s[i+1] == s[l-i-2] && s[i+2] != s[l-i-3]) {
            if (l-i-1 == i+2) t++;
            else t += 2;
            s[i] = s[l-i-1];
            s[i+2] = s[l-i-3];
        } else if (s[i] != s[l-i-1] && s[i+1] == s[l-i-2] && s[i+2] == s[l-i-3]) {
            t += 2;
            s[i] = s[l-i-1];
        }
    }
    cout << t << '\n';
}