#include <bits/stdc++.h>
#define rep(i, a) for (int i = 0; i < (a); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define repr(i, a) for (int i = (a) - 1; i >= 0; i--)
#define repr2(i, a, b) for (int i = (b) - 1; i >= (a); i--)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

int main() {
    string SA, SB, PA, PB, XA, XB;
    cin >> SA >> PA >> XA >> SB >> PB >> XB;

    if (PA.length() < PB.length()) PA = string(PB.length() - PA.length(), '0') + PA;
    if (PA.length() > PB.length()) PB = string(PA.length() - PB.length(), '0') + PB;

    if (PA == PB) {
        cout << -1 << endl;
    } else if (PA > PB) {
        cout << SA << endl;
    } else {
        cout << SB << endl;
    }
}