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

/**************************************************************
	Problem: 1002
	User: sz002
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/