#include <iostream>
#include <string>

using namespace std;

int main()
{
	string n, m;
	cin >> n >> m;

	if (n.size() > m.size())
		cout << n;
	if (n.size() < m.size())
		cout << m;

	if (n.size() == m.size())
	{
		for (unsigned long i = 0; i < n.size(); i++)
		{
			if (n[i] > m[i])
			{
				if (n[i] == '7' && m[i] == '4')
				{
					cout << m;
					break;
				}
				cout << n;
				break;
			}

			if (n[i] < m[i])
			{
				if (n[i] == '4' && m[i] == '7')
				{
					cout << n;
					break;
				}
				cout << m;
				break;
			}
		}

	}
	cout << endl;
	return 0;
}