#include <bits/stdc++.h>
using namespace std;
const long double Pi = 3.141592653;
const long long mod = 1e6 + 3;
class Graph {
  map<int, vector<int>> ma;

 public:
  void addedge(int n, int m) {
    ma[n].push_back(m);
    ma[m].push_back(n);
  }
};
int main() {
  long long n;
  cin >> n;
  long long i = n;
  long long ans = 0;
  long long p = 2, k = 1;
  ans = (1 + n) * n;
  ans = ans / 2;
  while ((n - p) > 0) {
    long long c = (n - p) * k;
    p++;
    k++;
    ans += c;
  }
  cout << ans;
  return 0;
}
