/* -*- coding: utf-8 -*-
 *
 * 71.cc: No.71 そろばん - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

typedef long long ll;

/* global variables */

/* subroutines */

/* main */

int main() {
  int n;
  cin >> n;

  ll maxsum = 0;

  for (int i = 1, j = n - 1; i < n; i++, j--) {
    ll sum = (ll)(i + 1) * j + i;
    if (maxsum < sum) maxsum = sum;
  }

  printf("%lld\n", maxsum);
  return 0;
}