#include<bits/stdc++.h> 
using namespace std;
int main()
{
    int s,n;
    cin>>s;
	n=(1+s)*s/2;
	cout<<n; 
	return 0;
}
/**************************************************************
	Problem: 1002
	User: zhangchenyu
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/