#include <bits/stdc++.h>

using namespace std;

unsigned long long gcd(unsigned long long a, unsigned long long b) {
	return b ? gcd(b, a % b) : a;
}

void hawawa()
{
	long long n;
	cin >> n;
	long long ans = 0;
	for (long long i = 0; i <= n; i++) {
		ans = max(ans, (n - i + 1) * i + n - i);
	}
	cout << ans << "\n";
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	hawawa();
	return 0;
}