#include <bits/stdc++.h>
using namespace std;
int main()
{
    string s, t, p, q;
    char c;
    cin >> s >> p >> c >> t >> q >> c;
    if (p == q) cout << -1 << endl;
    else if (p > q) cout << s << endl;
    else cout << t << endl;
    return 0;
}