#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	int s=(1+n)*(n/2);
	cout<<s;
}
/**************************************************************
	Problem: 1002
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/