#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
signed main(){
  string s,t,x,y;
  char c;
  cin>>s>>x>>c>>t>>y>>c;
  if(x==y){
    cout<<-1<<endl;
    return 0;
  }
  auto calc=
    [&](string x,string y){
      if(x.size()==y.size()) return x>y;
      return x.size()>y.size();
    };
  cout<<(calc(x,y)?s:t)<<endl;
  return 0;
}