#include <iostream>
#include <string>
#include <map>
using namespace std;
int main()
{
    map<int, string> a;
    string x, y;
    int z;
    cin>>x>>z>>y; a[z]=x;
    cin>>x>>z>>y; a[z]=x;
    cout<<(a.size()==1 ? "-1" : (++(a.begin()))->second)<<endl;
}