#include <stdio.h>
#include <string.h>

int main(void)
{
	char A[11], B[11];
	int A_length, B_length, i;
	scanf("%s%s", A, B);
	A_length = strlen(A);
	B_length = strlen(B);
	if (A_length > B_length) puts(A);
	else if (A_length < B_length) puts(B);
	else {
		for (i = 0; i < A_length; ++i) {
			if (A[i] == '4' && B[i] == '7') {
				puts(A);
				break;
			}
			else if (A[i] == '7' && B[i] == '4') {
				puts(B);
				break;
			}
			else if (A[i] > B[i]) {
				puts(A);
				break;
			}
			else if (A[i] < B[i]) {
				puts(B);
				break;
			}
		}
	}
	return 0;
}