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

int main() {
    string s;

    cin >> s;
    int len = s.length();
    int cnt = 0;

    int i = 0, j = len - 1;
    while (i < j) {
        if (s[i] == s[j]) {
            i++;
            j--;
        }

        else {
            if (j == i + 1 || j == i + 2) {
                cnt += 1;
                j--;
                i++;
            }
            else {
                cnt += 2;
                j-= 2;
                i+= 2;
            }
        }
    }
    cout << cnt << endl;
}