#include<cstdio>
#include<iostream>
#include<queue>
#include<algorithm>
#include<string>

using namespace std;



int main(){
	string sa, sb, pa, pb;
	char xa, xb; //どうでもよい

	cin >> sa >> pa >> xa >> sb >> pb >> xb;
	if (pa.length() > pb.length()){
		cout << sa << endl;
	}
	else if (pa == pb){
		puts("-1");
	}
	else if (pa.length()<pb.length()){
		cout << sb << endl;
	}
	else
	{

		int i = 0;
		while (i < pa.length())
		{
			if (pa[i] != pb[i])
			{
				cout << (pa[i] > pb[i] ? sa : sb) << endl;
				return 0;
			}
			i++;
		}
		cout << -1 << endl;
	}
	return 0;
}