#include <bits/stdc++.h>
using namespace std;
const int base = 1e9;
const int maxn = 100005;
const int MAXN = 1000000;
const int logn = 12;
const int inf = 2e9;
const int alpha = 26;
const int my_hash = 31;
const long long my_mod = 2674894331;
const long long l_inf = 4e18;
const long long mod = 1e9;
const double pi = acos(-1.0);
const double eps = 1e-8;
int main() {
  int n, ans = 0;
  scanf("%d", &n);
  for (int i = 1; i < n; i++) ans += i * (n - i);
  ans += n;
  printf("%d", ans);
}
