#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,cnt=0,b=1;
	cin>>n;
	for(int i=1;i<=n;i++){
		cnt+=i;
		i+=1;
	}
	cout<<cnt;
	return 0;
}
/**************************************************************
	Problem: 1003
	User: xuanhua
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/