#include <iostream>
#include <string>
using namespace std;
int main() {
	string Sa, Sb;
	string Pa, Pb;
	char Xa, Xb;
	cin >> Sa >> Pa >> Xa;
	cin >> Sb >> Pb >> Xb;
	long int size_a = Pa.length();
	long int size_b = Pb.length();

	if (size_a == size_b) {
		if (Pa == Pb) {
			cout << -1 << endl;
		}
		else{
			for (long i = 0; i < size_a;i++) {
				if (Pa[i] > Pb[i]) {
					cout << Sa << endl; break;
				}
				else if(Pa[i] < Pb[i]){
					cout << Sb << endl; break;
				}
			}
		}
	}
	else {
		cout << ((size_a > size_b) ? Sa : Sb )<< endl;
	}
	return 0;
}