#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-9;
const double PI = 3.1415926535897932384626433832795;
const int inf = 0x7f7f7f7f;
int main() {
  int n;
  scanf("%d", &n);
  int ans = 0;
  for (int i = 0; i < n; i++) {
    int cut = (n - i) * (i + 1);
    ans += cut;
  }
  int cut = (n - 1) * n;
  cut /= 2;
  printf("%d\n", ans - cut);
  return 0;
}
