#include <iostream>
//using namespace std;
typedef unsigned long long ul;
typedef signed long long ll;

int main(void)
{
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  std::string sa, sb, pa, pb, xa, xb;
  std::cin >> sa >> pa >> xa >> sb >> pb >> xb;
  if (pa == pb) std::cout << -1 << std::endl;
  else {
    if (pa.size() > pb.size()) std::cout << sa << std::endl;
    else if (pa.size() < pb.size()) std::cout << sb << std::endl;
    else if (pa > pb) std::cout << sa << std::endl;
    else std::cout << sb << std::endl;
  }
  return 0;
}