#include <stdio.h>

char a[11], b[11];

int len(char[]);
int comp(char, char);

int main(void) {
	scanf("%s %s", a, b);
	if( len(a) != len(b) ) { printf("%s\n", (len(a) < len(b) ? b : a) ); }
	else {
		int i = 0;
		while( comp(a[i], b[i]) == 0 ) { i++; }
		printf("%s\n", (comp(a[i], b[i]) == 1 ? b : a) );
	}
	return 0;
}

int len(char c[]) {
	int i = 0;
	while(c[i] != '\0') { i++; }
	return i;
}

int comp(char x, char y) {
	if(x == '7' && y == '4') { return  1; }
	if(x == '4' && y == '7') { return -1; }
	if(x == y) { return 0; }
	return (x < y ? 1 : -1);
}