#include <bits/stdc++.h>
using namespace std;
int n, t;
long long res = 0;
char a[51];
int main() {
  cin >> n;
  int ans = 0;
  for (int i = n; i > 0; i--) {
    res += (i * (n - i + 1)) - (n - i);
  }
  cout << res << endl;
  return 0;
}
