#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
int main() {
    string SA, SB, PA, PB;
    char XA, XB;
    cin >> SA >> PA >> XA;
    cin >> SB >> PB >> XB;

    // Output
    if (PA == PB) {
        cout << -1 << endl;
    } else if (PA.size() > PB.size()) {
        cout << SA << endl;
    } else if (PA.size() < PB.size()) {
        cout << SB << endl;
    } else {
        int N = PA.size();
        rep(i, N) {
            if (PA[i] == PB[i]) {
                continue;
            } else if (PA[i] > PB[i]) {
                cout << SA << endl;
                return 0;
            } else {
                cout << SB << endl;
                return 0;
            }
        }
    }
}