#include <iostream>
#include <string>
#include <stdio.h>

using namespace std;

int main(int argc, char* argv[]) {

	int n, sum = 0, b = 1;
	cin >> n;

	while (b < n) {
		sum += b + n;
		b++;
		n--;
	}
	if (b == n) {
		sum += b;
	}
	
	cout << sum;

	return 0;
}