#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
typedef long long ll;

int main(){
  string a, b;
  string aa, bb;
  cin >> a >> b;
  aa = a; bb = b;
  ll A = 0, B = 0;
  int len = min(a.length(), b.length());
  int ai = a.length() - 1;
  int bi = b.length() - 1;
  while(len > 0){
    if(a[ai] == '4' && b[bi] == '7') a[ai] = '8';
    if(a[ai] == '7' && b[bi] == '4') b[bi] = '8';
    ai--;
    bi--;
    len--;
  }
  FOR(i,0,a.length()){
    A *= 10;
    A += a[i];
  }
  FOR(i,0,b.length()){
    B *= 10;
    B += b[i];
  }
  cout << (A > B ? aa : bb) << endl;
  return 0;
}