use strict;
use warnings;
use utf8;
use List::Util qw(min);

my ($A, $B) = ($ARGV[0], $ARGV[1]);
my $max = 0;

for (my $i = 0; $i <= $A; $i++) {
    for (my $j = 0; $j <= $B; $j++) {
        my $min = min($i, $j, ($i^$j));
        if ($min > $max) {
            $max = $min;
        }
    }
}
print "$max\n";