#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
typedef long long ll;

bool comp(string a, string b){
  int len_a = a.length();
  int len_b = b.length();
  if(len_a > len_b) return true;
  else if(len_a < len_b) return false;
  FOR(i,0,len_a){
    if(a[i] != b[i]){
      return a[i] > b[i];
    }
  }
  return true;
}

int main(){
  string sa, pa, xa;
  string sb, pb, xb;
  cin >> sa >> pa >> xa;
  cin >> sb >> pb >> xb;
  if (pa == pb) cout << -1 << endl;
  else if(comp(pa, pb)) cout << sa << endl;
  else cout << sb << endl;
  return 0;
}