#include<iostream>
#include<string>
#include<fstream>
#include<iomanip>
#include<vector>
#include<cctype>
#include<algorithm>
#include<sstream>
using namespace std;

int main()
{
	string s, t;
	cin >> s >> t;
	int a = static_cast<int>(s.size()), b = static_cast<int>(t.size());
	if (a > b)cout << s << endl;
	else if (a < b)cout << t << endl;
	else
	{
		for (int i = 0; i < a; i++)
		{
			if (s[i] == t[i])continue;
			else
			{
				if (s[i] == '4'&&t[i] == '7')
				{
					cout << s << endl;
				}
				else if (s[i] == '7'&&t[i] == '4')
				{
					cout << t << endl;
				}
				else
				{
					if (s[i]>t[i])cout << s << endl;
					else cout << t << endl;
				}
				break;
			}
		}
	}
	return 0;
}