#include <bits/stdc++.h>
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]) {
				cout << a << endl;
				return 0;
			}
			else if (a[i] < b[i]) {
				cout << b << endl;
				return 0;
			}
		}
	}

	return 0;
}