#include<bits/stdc++.h>
using namespace std;
int n,s;
int main(){
	cin>>n;
	while(n>=0){
		s+=n;
		n--;
	}
	cout<<s;
	return 0;
}
/**************************************************************
	Problem: 2100
	User: zhangziang
	Language: C++
	Result: Accepted
	Time:41 ms
	Memory:2072 kb
****************************************************************/