#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	string a, b;
	cin >> a >> b;
	if(a.length() > b.length()) {
		cout << a << endl;
	}
	else if(a.length() < b.length()) {
		cout << b << endl;
	}
	else {
		for(int i = 0; i < a.length(); 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 if(a[i] > b[i]) {
					cout << a << endl;
				}
				else {
					cout << b << endl;
				}
				break;
			}
		}
	}
}