#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int a, b;
  cin >> a >> b;
  string x = to_string(a), y = to_string(b);

  if (x.length() > y.length())
    cout << x << endl;
  else if (x.length() < y.length())
    cout << y << endl;
  else {
    for (int i = 0; i < x.length(); i++) {
      if (x[i] == y[i]) continue;
      if (x[i] == '4' && y[i] == '7')
        cout << x << endl;
      else if (x[i] == '7' && y[i] == '4')
        cout << y << endl;
      else if (x[i] > y[i])
        cout << x << endl;
      else
        cout << y << endl;
      break;
    }
  }
  
  return 0;
}