Создать односвязный кольцевой линейный список элементы которого целые числа

#include <iostream>
 
using namespace std;
 
struct List {
  int data;
  List* next;
};
 
void add(List*& head, List*& tail, int what) {
  List* new_one = new List;
 
  new_one->data = what;
 
  if (!head && !tail) {
    head = new_one;
    tail = new_one;
    new_one->next = new_one;
  } else {
    tail->next = new_one;
    tail = new_one;
    new_one->next = head;
  }
}
 
void del(List*& head, List*& tail, List*& what) {
  if (head == tail) {
    delete what;
  } else if (head == what) {
    List* tmp = head;
    
    head = head->next;
 
    delete tmp;
  } else if (tail == what) {
    List* tmp_2 = head;
 
    while (tmp_2->next != tail)
      tmp_2 = tmp_2->next;
 
    List* tmp = tail;
 
    tmp_2->next = head;
    tail = tmp_2;
 
    delete tmp;
  } else {
    List* before = head;
 
    while (before->next != what)
      before = before->next;
 
    before->next = what->next;
 
    delete what;
  }
}
 
int32_t main() {
  List* head = nullptr;
  List* tail = nullptr;
 
  int n;
  cin >> n;
 
  for (int i = 0; i < n; ++i) {
    int t;
    cin >> t;
 
    add(head, tail, t);
  }
 
  while (n > 2) {
    List* for_del = head;
    
    for (int i = 0; i < 2; ++i)
      for_del = for_del->next;
 
    del(head, tail, for_del);
    
    --n;
  }
 
  cout << head->data + head->next->data;
}