//Normal

#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

void print(auto a){
  cout << a;
}

void prints(auto a){
  cout << a << " ";
}

void prints(){
  cout << " ";
}

void printl(auto a){
  cout << a << endl;
}

void printl(){
  cout << endl;
}

void fix(int n){
  cout << fixed << setprecision(n);
}

int main(){
  string SA, PA, XA, SB, PB, XB; cin >> SA >> PA >> XA >> SB >> PB >> XB;
  
  if(PA == PB){
    printl(-1);
  }else{
    int jud;
    int pa = (int)PA.size();
    int pb = (int)PB.size();
    
    if(pa == pb){
      for(int i = 0; i < pa; i++){
        if(PA[i] == PB[i]) continue;
        
        PA[i] > PB[i] ? jud = 1 : jud = -1;
        break;
      }
    }else{
      pa > pb ? jud = 1 : jud = -1;
    }
    
    jud == 1 ? printl(SA) : printl(SB);
  }
  
  return 0;
  
}