#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, cnt = 0;
  int arr[200004];
  cin >> n;
  for (int i = 0; i < n; i++) arr[i] = i;
  cnt += n * (n - 1) / 2;
  for (int j = n - 1; j > 0; j--) {
    for (int i = 0; i < j; i++) cnt += arr[i];
    cnt++;
  }
  cnt++;
  cout << cnt << endl;
  return 0;
}
