//如果你不想用高精度算法，这可以帮助拿到这道题的分数
#include<bits/stdc++.h>
using namespace std;
int main()
{
	freopen("jia.in","r",stdin);
	freopen("jia.out","w",stdout);
	unsigned long long b;
	cin>>b;
	cout<<(1+b)*b/2;
}