sub str2val {
    my ($str) = @_;
    my %convert = (A => 1, B => 6, C => 31, D => 156, E => 781, F => 3906);
    my $val = 0;
    for my $char (split //, $str) {
        $val += $convert{$char};
    }
    return $val;
}

sub val2str {
    my ($val) = @_;
    my %convert = (A => 1, B => 6, C => 31, D => 156, E => 781, F => 3906);
    my $str = '';
    return $str if $val < 1;
    for my $char (sort {$convert{$b} <=> $convert{$a}} keys %convert) {
        my $count = int($val / $convert{$char});
        $str .= ($char x $count);
        $val %= $convert{$char};
    }
    return $str;
}