#include <bits/stdc++.h> 
using namespace std;
int main() {
	int a,n;
	cin>>n;
	a=(1+n)*n/2;
	cout<<a; 
	
	
	
	
} 
/**************************************************************
	Problem: 1002
	User: zhuangwenya
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/