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

int main(){
  string A, B; cin >> A >> B;
  int a = (int)A.size(), b = (int)B.size();
  if(a != b){
    if(a > b) cout << A << endl;
    else cout << B << endl;
  }else{
    for(int i = 0; i < a; i++){
      if(A[i] == B[i]) continue;
      if(A[i] > B[i]){
        if(A[i] == '7' and B[i] == '4') cout << B << endl;
        else cout << A << endl;
        return 0;
      }else{
        if(A[i] == '4' and B[i] == '7') cout << A << endl;
        else cout << B << endl;
        return 0;
      }
    }
  }
}