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// Jan Zachar 03/12/22
#include <iostream>
#include <string>
#define check(x) (str[x] == str[str.length()-1-x])


using namespace std;

string str;
int cntr;

int main() {
    ios_base::sync_with_stdio(false);
    cout.tie(nullptr);
    cin.tie(nullptr);

    cin >> str;

    for (int i = 0; i < str.length()-1; i++) {
        if (check(i)) continue;
        else if (str[i] != str[i+1]) {
            swap(str[i], str[i+1]);
            cntr++;
        }
    }

    for (int i = str.length()-1; i > 0; i--) {
        if (check(i)) continue;
        else if (str[i] != str[i-1]) {
            swap(str[i], str[i-1]);
            cntr++;
        }
    }

    for (int i = 0; i < str.length()-1; i++) {
        if (!check(i)) {
            cout << -1 << endl;
            return 0;
        }
    }

    cout << cntr << endl;
    return 0;
}