#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;

int main(){
	string a,b,c,d;
	string pa,pb;
	cin >> a >> pa >> c;
	cin >> b >> pb >> d;
	if( pa == pb ){
		cout << -1 << endl;
		return 0;
	}
	if( pa.size() == pb.size()){
		for(int i = 0; i < pa.size(); i++){
			if(pa[i] == pb[i]) continue;
			if(pa[i] > pb[i]) cout << a << endl;
			else cout << b << endl;
		}
	}
	else if( pa.size() > pb.size() ) cout << a << endl;
	else cout << b << endl;
	return 0;
}