#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  scanf("%d", &n);
  long long tot = 0;
  for (int i = 1; i <= n; i++) {
    tot += (long long)(n - i) * i + 1ll;
  }
  printf("%I64d\n", tot);
  return 0;
}
