#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000000LL

int main(){
	
	long long n;
	cin>>n;
	unsigned long long x = n;
	unsigned long long y = n+1;
	if(x%2==0)x/=2;
	else y/=2;
	x *= y;
	cout<<x<<endl;
	
	return 0;
}