#include <iostream>
using namespace std;
int main(){
  string a,b;
  cin>>a>>b;
  int as=a.size();
  int bs=b.size();
  string s;
  if(as>bs){
    s=a;
  } else if(as<bs){
    s=b;
  } else {
    for(int i=0; i<a.size(); ++i){
      char ca=a[i];
      char cb=b[i];
      if(ca=='4' && cb=='7'){
        s=a;
        break;
      } else if(ca=='7' && cb=='4'){
        s=b;
        break;
      } else if(ca>cb){
        s=a;
        break;
      } else if(ca<cb){
        s=b;
        break;
      } else if(ca==cb){
        //pass
      }
    }
  }
  cout<<s<<endl;
  return 0;
}