#include <algorithm>
#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
#include <map>
#define rep(i,n) for (int i=0; i<n; ++i)
#define FOR(i,a,b) for (int i=a; i<b+1; ++i)
#define pb(x) push_back(x)
#define ll long long
using namespace std;

int main () {
  string a,b,tmp,pa,pb;
  cin>> a >> pa >> tmp >> b >> pb >> tmp;
  if (pa.size() > pb.size())  {
    cout << a << endl;
  } else if (pa.size() < pb.size()) {
    cout << b << endl;
  } else if (a == b) {
    cout << -1 << endl;
  } else {
    rep(i,pa.size()) {
      if (pa[i] > pb[i]) {
        cout << a << endl;
        break;
      } else if (pa[i] < pb[i]) {
        cout << b << endl;
        break;
      }
    }
  }
  return 0;
}