def nth_to_last_node(n,head):

    left_pointer = head
    right_pointer = head

    for i in range(n-1):

        if not rightpointer.nextnode:
            raise LookupError("Error: n is larger than the linked list")

        right_pointer = right_popinter.nextnode

    while right_pointrt.nextnode:
        left_pointer = left_pointer.nextnode
        right_pointer = right_pointer.nextnode

    return left_pointer