#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

// a < b: -1
// a == b: 0
// a > b: +1
inline int comp(string a, string b) {
  if (a.size() < b.size()) return -1;
  if (a.size() > b.size()) return 1;
  if (a == b) return 0;
  if (a < b) return -1;
  return 1;
}

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