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

int main(){
	int n;
	int hoge;
	int sum = 0;
	cin >>n;
	if(n%2==0)hoge = n/2;
	else hoge = n/2+1;
	for(int i=0; i<hoge; ++i){
		sum += i+2;
		if(i+1< hoge)
		sum += i+2;
	}
	cout << sum << endl;
	return 0;
}