sub parse {
    my ($sequence) = @_;
    $sequence =~ s/[^0123]//g; # leave just digits
    $sequence =~ s/1032$//; # remove identifier at the end, if any
    die "Sequence should contain 8 or 12 quaternary digits" unless $sequence =~ m/^([0123]{4})([0123]{4})$/;

    my $byte = quad2dec($1);
    return -1 unless ($byte & 192) == 192; # two higer bits must be set
    #print "{$byte}";

    $byte &= 63; # use 6 leftmost bits
    my $checksum = $checksums[$byte];
    return -1 unless ($checksum == $2); # checksums must match

    #print "<$1><$2>=<$byte><$checksum>\n";

    return $byte;
}