use strict;
use warnings;

my ($x, $y) = split / /, <>;
my @m = split //, $x;
chomp $y;
my @n = split //, $y;

if($#m == $#n) {
	for(my $i = 0; $i < $#n + 1; $i++) {
		if(($m[$i] == 4)&&($n[$i] == 7)) {
			print @m;
			print "\n";
			last;
		} elsif(($m[$i] == 7)&&($n[$i] == 4)) {
			print @n;
			print "\n";
			last;
		} elsif($m[$i] < $n[$i]) {
			print @n;
			print "\n";
			last;
		} elsif($m[$i] > $n[$i]) {
			print @m;
			print "\n";
			last;
		}
	}
} elsif($#m < $#n) {
	print @n;
	print "\n";
} else {
	print @m;
	print "\n";
}
exit;