#include <bits/stdc++.h>

//const static double	de_PI	= 3.14159265358979323846;
//const static int	de_MOD	= 1000000007;
//const static int	de_MAX	= 999999999;
//const static int	de_MIN = -999999999;

int main(void) {

	//std::ifstream in("123.txt");	std::cin.rdbuf(in.rdbuf());	

	std::string A, B;
	std::cin >> A >> B;

	if (A.length() > B.length()) {
		std::cout << A << std::endl;
		return 0;
	}
	if (A.length() < B.length()) {
		std::cout << B << std::endl;
		return 0;
	}

	int i = 0;
	while (A[i] == B[i]) { i++; }

	if (A[i] == '4' && B[i] == '7') {
		std::cout << A << std::endl;
		return 0;
	}
	
	if (A[i] == '7' && B[i] == '4') {
		std::cout << B << std::endl;
		return 0;
	}

	if (A[i] > B[i]) {
		std::cout << A << std::endl;
	}
	else {
		std::cout << B << std::endl;
	}
}