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

/**************************************************************
	Problem: 1002
	User: zy002
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/