/* -*- coding: utf-8 -*-
 *
 * 2937.cc:  No.2937 Sigma Plus Problem - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

/* typedef */

using ull = unsigned long long;

/* global variables */

/* subroutines */

/* main */

int main() {
  ull n;
  scanf("%llu", &n);

  ull s = (n & 1) ? n * ((n + 1) / 2) : (n / 2) * (n + 1);
  printf("%llu\n", s);
  
  return 0;
}