#include <iostream>
using namespace std;

#define int long long
signed main() {
	
	int N;
	cin>> N;
	
	int ans=0;
	for(int i=0; i<=N; i++){
		ans=max(ans, i*(N-i+1)+(N-i));
	}
	
	cout<< ans<< endl;
	
	return 0;
}