#include<iostream>
#include<string>
using namespace std;
int main(void){
	string sa, sb, pa, pb; char x;
	cin >> sa >> pa >> x >> sb >> pb >> x;
	if (pa.length() != pb.length()){
		cout << (pa.length() < pb.length() ? sb : sa) << endl;
	}
	else if (pa != pb){
		cout << (pa < pb ? sb : sa) << endl;
	}
	else{ cout << -1 << endl; }
	return 0;
}