#include<iostream>
#include<vector>
#include <string>
using namespace std;
int main() {
	string n1,n2;
	cin >> n1 >> n2;
	if (n1.size() > n2.size())
	{
		cout << n1 << endl;
	}
	else if(n1.size() < n2.size())
	{
		cout << n2 << endl;
	}
	else
	{
		for (int i = 0; i < n1.size(); i++)
		{
			if (n1[i] == '4' && n2[i] == '7')
			{
				cout << n1 << endl;
				break;
			}
			else if (n1[i] == '7' && n2[i] == '4')
			{
				cout << n2 << endl;
				break;
			}
			else if (n1[i] > n2[i])
			{
				cout << n1 << endl;
				break;
			}
			else if (n1[i] < n2[i])
			{
				cout << n2 << endl;
				break;
			}
		}
	}
}