/* -*- coding: utf-8 -*-
 *
 * 293.cc: No.293 4>7の世界 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 10;

/* typedef */

/* global variables */

int das[MAX_N], dbs[MAX_N];

/* subroutines */

/* main */

int main() {
  string sa, sb;
  cin >> sa >> sb;

  int na = sa.size(), nb = sb.size();
  int n = max(na, nb);

  for (int i = 0; i < na; i++) das[n - na + i] = sa[i] - '0';
  for (int i = 0; i < nb; i++) dbs[n - nb + i] = sb[i] - '0';
  //for (int i = 0; i < n; i++) printf("%d", das[i]); putchar('\n');
  //for (int i = 0; i < n; i++) printf("%d", dbs[i]); putchar('\n');

  bool ab = true;
  for (int i = 0; i < n; i++) {
    if (das[i] == dbs[i]) continue;

    if (das[i] == 7 && dbs[i] == 4) ab = false;
    else if (das[i] == 4 && dbs[i] == 7) ab = true;
    else ab = (das[i] >= dbs[i]);
    break;
  }

  cout << (ab ? sa : sb) << endl;
  return 0;
}