#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

string sa, sb, pa, pb;
char xa, xb;

int comp(string a, string b) {
  if (a.size() == b.size()) {
    if (a == b) return 0;
    else if (a > b) return 1;
    else return -1;
  } else if (a.size() > b.size()) return 1;
  else return -1;
}

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