struct node *count_out( struct node *head, unsigned n )
{
    assert( head );

    unsigned length = 1;
    struct node *prev = head,
                *next = head->next;

    while ( next != head )
    {
        prev = next;
        next = next->next;
        ++ length;
    }

    while ( length > 1 )
    {
        for ( unsigned m = n % length; m > 0; --m )
        {
            prev = next;
            next = next->next;
        }

        next = next->next;
        prev->next = next;
        -- length;
    }

    assert( next->next == next );

    return next;
}