#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000

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