#include<bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

#define rep(i, a, b) for(ll i = (ll)a; i < (ll)b; i++)
#define irep(i, v) for(auto i = (v).begin(); i != (v).end(); i++)
#define ALL(v) (v).begin(), (v).end()
#define SZ(v) (ll)(v).size()

const ll INF = 1e18;
const ld EPS = 1e-10;


int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  srand((unsigned)time(NULL));
  cout << fixed << setprecision(20);

  string s, t;
  cin >> s >> t;

  if(s.size() > t.size()) cout << s << endl;
  else if(s.size() < t.size()) cout << t << endl;
  else{
    for(ll i = 0; i < s.size(); i++){
      if(s[i] == '4' && t[i] == '7'){
        cout << s << endl;
        return 0;
      }
      else if(s[i] == '7' && t[i] == '4'){
        cout << t << endl;
        return 0;
      }
      else{
        if(s[i] < t[i]){
          cout << t << endl;
          break;
        }
        else if(s[i] > t[i]){
          cout << s << endl;
          return 0;
        }
      }
    }
    cout << s << endl;
  }


  return 0;
}