#include <iostream>
#include <math.h>
#include <string>
#include <algorithm>
using namespace std;

int main(){
	long long n;
	long long a;
	long long ans;
	cin >> n;
	a = n / 2;
	ans = (a + 1)*(n - a) + a;
	cout << ans << endl;
	return 0;
}