def nth_to_last_node(n,head):

    left_pointer = head
    right_pointer = head

    for i in range(n-1):

        if not right_pointer.nextnode:

            raise LookupError('Error:n is larger than the linked list')
            right_pointer = right_pointer.nextnode

        while right_pointer.nextnode:

            left_pointer = left_pointer.nextnode
            right_pointer = right_pointer.nextnode

    return left_pointer