/* -*- coding: utf-8 -*-
 *
 * 201.cc: No.201 yukicoderじゃんけん - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  string sa, pa, xa;
  string sb, pb, xb;
  cin >> sa >> pa >> xa >> sb >> pb >> xb;

  int na = pa.size(), nb = pb.size();

  int cmp = -1;
  if (na > nb) cmp = 0;
  else if (na < nb) cmp = 1;
  else {
    for (int i = 0; i < na; i++)
      if (pa[i] != pb[i]) {
	cmp = (pa[i] > pb[i]) ? 0 : 1;
	break;
      }
  }

  cout << ((cmp == -1) ? "-1" : (cmp == 0) ? sa : sb) << endl;
  return 0;
}