#include <iostream>
#include <algorithm>
#include <string>
#include <cstring>
using namespace std;

#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)
#define SQR(X) ((X)*(X))

typedef long long ll;
typedef unsigned long long ull;
typedef long double lb;
/* ここからが本編 */
int main(void)
{
  int i,j,k,l;
  int n;
  char a[20];
  char b[20];
  int ans = 0;/* 0のときaが大きい */
  cin >> a >> b;
  if(strlen(a) < strlen(b) ) ans = 1;
  else if(strlen(a) > strlen(b) ) ;
  else {
    for(i=0;;i++) {
      if(a[i] == '7' && b[i] == '4') {
        ans = 1; break;
      }
      if(a[i] == '4' && b[i] == '7') break;
      if(a[i] > b[i] ) break;
      if(a[i] < b[i] ) {
        ans = 1;
        break;
      }
    }
  }
  if(ans) cout << b << endl;
  else cout << a << endl;

  
  return 0;
}