#include<bits/stdc++.h>
using namespace std;

int main(){
	cin.tie(0),ios::sync_with_stdio(false);
	string a,b,aa,bb; char g; cin>>a>>aa>>g>>b>>bb>>g;
	if(aa.size()>bb.size())cout<<a;
	else if(bb.size()>aa.size())cout<<b;
	else if(aa>bb)cout<<a;
	else if(bb>aa)cout<<b;
	else cout<<-1;
	cout<<"\n"s;
}