use strict;
use warnings;
use utf8;

my $arg = <STDIN>;
chomp $arg;
my ($A, $B) = split /\s/, $arg;
my $max = 0;

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