#include <iostream>
#include <algorithm>

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] != b[i]) {
                if (a[i] == '4' && b[i] == '7')cout << a << endl;
                else if (a[i] == '7' && b[i] == '4')cout << b << endl;
                else cout << (a[i] > b[i] ? a : b) << endl;
                break;
            }
        }
    }
    return 0;
}