use List::Util qw( sum );
my $input = '000181080002020202020202';
my $sum = sum map { hex } split /([a-f0-9]{2})/, $input;
my $xored_sum = 0xff ^ $sum;
printf "hex of %d: %X\n", $xored_sum, $xored_sum;
__END__
hex of 103: 67