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

using namespace std;

int l, t, f;
string s;

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