#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <fstream>
#include <sstream>
#include<set>
#include<stack>
#include<time.h>
#include <sys/types.h>
#include <tuple>
#include <numeric>
#include <iterator>

typedef long long int ll;
//#include<bits/stdc++.h>


using namespace std;

ll gcd(ll a, ll b) {
    if (a < b)swap(a, b);
    if (b == 0)return a;
    return gcd(b, a % b);
}
int lcm(int a, int b) {
    return a * b / gcd(a, b);
}


int main()
{

    int Q;
    Q = 1;
    //cin >> Q;


    while (Q--) {
        string a, b;
        cin >> a >> b;
        if (a.size() > b.size())cout << a;
        else if (a.size() < b.size())cout << b;
        else {
            for (int i = 0; i < a.size(); i++) {
                if (a[i] == b[i])continue;
                if (a[i] == '4' && b[i] == '7')cout << a;
                else if (b[i] == '4' && a[i] == '7')cout << b;
                else if (a[i] > b[i])cout << a;
                else cout << b;
                return 0;
            }

        }
       
    }
    return 0;
}