#include <iostream>
#include <cstdio>
#include <string>
#include <sstream>
#include <algorithm>
#include <math.h>
#include <map>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#define PI 3.14159265359
#define INF 99999999;
#define rep(i, n) for(int i=0; i<n; i++)
#define REP(n) rep(i, n)
#define EPS 1e-10
typedef long long ll;
using namespace std;



/*
class Target
{
public:
	vector <string> draw(int n)
	{

	}
};
*/



int main()
{
	int N;
	ll max_num = 0;
	
	cin >> N;
	for (ll i=0; i<=N; i++)	//iは上の珠の数
	{
		if (max_num < (ll)((N-i+1)*i+(N-i)))
		{
			max_num = (ll)((N-i+1)*i+(N-i));
		}
	}
	
	cout << max_num << endl;
	
	return 0;
}