#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>

using namespace std;


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