code: def rotate_right(head, k):
      
      if not head or not head.next:
          return head
      current = head
      length = 1
      # count length of the list
      while current.next:
          current = current.next
          length += 1
      # make it circular
      current.next = head
      k = k % length
      # rotate until length-k
      for i in range(length-k):
          current = current.next
      head = current.next
      current.next = None
      return head
docs: :type head: ListNode
      :type k: int
      :rtype: ListNode