#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, result, i, j;
  scanf("%lld", &n);
  result = n * (n + 1) / 2;
  j = n - 2;
  for (i = 1; i <= n - 2; i++, j--) {
    result += i * j;
  }
  printf("%lld", result);
  return 0;
}
