#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define llong long long

int main() {
    llong aa, bb;
    cin >> aa >> bb;
    string a = to_string(aa);
    string b = to_string(bb);

    if(a.length() == b.length()) {
        bool awin;
        rep(i, a.length()) {
            int ai = stoi(""s + a[i]);
            int bi = stoi(""s + b[i]);
            if(ai == bi) continue;
            awin = ai > bi;
            if(ai == 7 && bi == 4) awin = false;
            else if(ai == 4 && bi == 7) awin = true;
            break;
        }
        if(awin) {
            cout << a << "\n";
        } else {
            cout << b << "\n";
        }
    } else if(a.length() > b.length()) {
        cout << a << "\n";
    } else {
        cout << b << "\n";
    }
}