#include<bits/stdc++.h>
using namespace std;
int main() {
	int n,i,h=0;
	cin>>n;
	for(i=n;i>=0;i--){
		h=h+i;
	}
	cout<<h;
    return 0;
}
/**************************************************************
	Problem: 2100
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:37 ms
	Memory:2072 kb
****************************************************************/