void insertAtPosition(node *&head, node *&tail, int position, int d) {
  // insert at start
  if (position == 1) {
    insertAtHead(head, tail, d);
    return;
  }
  node *temp = new node(d);
  node *curr = head;
  int cnt = 1;
  while (cnt < position - 1) {
    curr = curr->next;
    cnt++;
  }
  // insert at last
  if (curr->next == NULL) {
    insertAtTail(tail, head, d);
    return;
  } else {
    temp->next = curr->next;
    curr->next = temp;
    temp->prev = curr;
    curr->next->prev = temp;
  }
}