@stack=qw(d b f a e c 6);  # <-- bottom .. top -->

##</code><code>##

@stack=qw(f e d c b a 6);  # <-- bottom .. top -->

##</code><code>##

# You are not allowed to modify this.
sub rotate_up {
        local($a,$b);
        $a=$_[0];
        $a--;
        return if $a<1;
        $b=pop @stack;
        splice(@stack, -$a, 0, $b);
}