sub scramble {
    (my $str, my $toshuf) = @_;
    my $len = length($str);
    if($toshuf * 2 > $len){
        return "!error-rorre!";
    }
    $str = lc($str);
    my @idx = ();
    my $i = $toshuf;
    push(@idx, $i--) while $i;
    push(@idx, ($toshuf + 1) .. ($len - $toshuf));
    push(@idx, $len - $i++) while $i < $toshuf;

    return sprintf(join("", map({"%$_\$s"} @idx)), split(//, $str));
}