#include<bits/stdc++.h>
using namespace std;
int n;

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin>>n;cout<<(1+n)*((n-1)/2+1)/2;
	return 0;
}

/**************************************************************
	Problem: 1003
	User: liangshinan
	Language: C
	Result: Compile Error
****************************************************************/