#include <bits/stdc++.h>
using namespace std;
int main(){
	int a,i,t;
	cin>>a;
	t=0;
	for(i=1;i<=a;i++) t=i+t;
	cout<<t;
	return 0;
	}

/**************************************************************
	Problem: 1002
	User: ljl2
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/