#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <deque>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <cassert>
 
using namespace std;
 
#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(long long i=(a);i<(b);++i)
#define clr(a, b) memset((a), (b) ,sizeof(a))
 
#define MOD 1000000007

int main(){
  int a,b;
  cin>>a>>b;
  long long n1 = max(a,b);
  long long n2 = min(a,b);
  for(long long i = 10000000000L; i > 0; i /= 10){
    int nb1 = n1/i%10;
    int nb2 = n2/i%10;
    if(nb1==7&&nb2==4){
      cout << n2 << endl;
      break;
    }
    else if(nb1>nb2){
      cout << n1 << endl;
      break;
    }
    else if(nb1<nb2){
      cout << n2 << endl;
      break;
    }
  }
  return 0;
}