#include "bits/stdc++.h"
using namespace std;

bool f(int x, int y) {
    if (x == 4 && y == 7 || x == 7 && y == 4) {
        swap(x, y);
    }
    return x > y;
}

int main() {
    string a, b; cin >> a >> b;
    if (a.size() != b.size()) {
        cout << (a.size() > b.size() ? a : b) << "\n";
        return 0;
    }
    if (a == "0" || b == "0") {
        cout << (a == "0" ? b : a) << "\n";
        return 0;
    }

    string aa = a, bb = b;
    reverse(a.begin(), a.end());
    reverse(b.begin(), b.end());
    int64_t x = stoll(a), y = stoll(b);
    while (x || y) {
        int b1 = x % 10, b2 = y % 10;
        x /= 10; y /= 10;
        if (b1 == b2) continue;
        cout << (f(b1, b2) ? aa : bb) << "\n";
        break;
    }

    return 0;
}