#include <bits/stdc++.h>
#include<iostream>
#include<iomanip>
#include<string>
#include<algorithm>
#include<vector>
#include<set>
#include<list>
#include<queue>
#include<math.h>
#include<bitset>
using ll = long long;
using namespace std;

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