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