#include<iostream>
#include<algorithm>
using namespace std;

int main(void)
{
	long long int n;
	long long int ans = 1;

	cin >> n;

	for (long long int i = 1; i < n; i++) {
		ans = max(ans, i + (n - i)*(i + 1));
	}

	cout << ans << endl;

	return 0;
}