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

/**************************************************************
	Problem: 1002
	User: ccf
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/