#include <bits/stdc++.h>
int main() {
  int n, i, result;
  while (scanf("%d", &n) != EOF) {
    result = 0;
    n++;
    for (i = 1; i <= n; i++) result += i * (n - i + 1);
    printf("%d\n", result);
  }
  return 0;
}
