void deleteNode (node* &head, node* &tail, int position) {
  // delete first node
  if (position == 1) {
    node* temp = head;
    temp -> next -> prev = NULL;
    head = temp -> next;
    temp -> next = NULL;
    delete temp;
    return;
  }
  node* curr = head;
  node* back = NULL;
  int cnt = 1;
  while (cnt < position) {
    back = curr;
    curr = curr -> next;
    cnt++;
  }
  //delete last node 
  if (curr -> next == NULL) {
    tail = back;
    back -> next = NULL;
    curr -> prev = NULL;
    delete curr;
    return;
  }
  // delete in between node 
  back -> next = curr -> next;
  curr -> next -> prev = back;
  curr -> next = NULL;
  curr -> prev = NULL;
  delete curr;
}