#include<bits/stdc++.h>

using namespace std;
using ll=long long;
#define rep2(i, a, n) for(int i = (a); i < (n); i++)
#define rep(i, n) rep2(i,0,n)

int main(){
  cin.tie(nullptr);ios_base::sync_with_stdio(false);
  string sa,sb,pa,pb;
  char xa,xb;
  cin>>sa>>pa>>xa;
  cin>>sb>>pb>>xb;
  if(pa==pb){
    cout<<-1<<endl;
    return 0;
  }
  if(pa.size()>pb.size()){
    cout<<sa<<endl;
    return 0;
  }else if(pa.size()<pb.size()){
    cout<<sb<<endl;
    return 0;
  }
  rep(i,pa.size()){
    if(pa[pa.size()-1-i]>pb[pa.size()-1-i]){
      cout<<sa<<endl;
      return 0;
    }else if(pa[pa.size()-1-i]<pb[pa.size()-1-i]){
      break;
    }
  }
  cout<<sb<<endl;
}