#include <bits/stdc++.h>
using namespace std;
int main () {
    string S;
    cin >> S;
    int N = S.size();
    for (int i = 0; i < N / 2 - 1; i ++) {
        if (S[i] != S[i + 1]) {
            cout << N - 2 << endl;
            return 0;
        }
    }
    cout << (N % 2 ? -1 : 0) << endl;
}