#include <bits/stdc++.h>

using namespace std;
using ll = long long;

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

    string s, t;
    cin >> s >> t;

    const int n = size(s), m = size(t);

    if (t[0] == '1') {
        char x = '0' ^ '1';
        for (char &c : s) {
            c ^= x;
        }
        for (char &c : t) {
            c ^= x;
        }
    }

    if (m == 1) {
        cout << (s.find(t) == string::npos ? 0 : -1) << '\n';
        return 0;
    }

    if (m == 2) {
        if (t[0] == t[1]) {

        } else {

        }
    }

    return 0;
}