sub collatz-step (Int $n) {
    if $n%%2 {
        return $n div 2;
    }
    else {
        return 3*$n+1;
    }
}

sub collatz-iter (Int $m) {
    my $n = $m;
    while $n>1 {
        $n = collatz-step $n;
        say $n;
     }
}