#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
typedef long long ll;

int main(){
  ll N;
  cin >> N;
  // 上の数i
  ll ans = 0;
  for (ll i = 0; i <= N + 1; i++) {
    ans = max(ans, (N - i + 1) * i + (N - i));
  }
  cout << ans << endl;
  return 0;
}