学步园

#include <iostream>
#include <cstring>
#include <cstdio>

using namespace std;

/**
int main()
{
	int a, b;
	while (~scanf("%d %d", &a, &b))
	{
		cout<<a+b<<endl;
	}
	return 0;
}
*/


void Sum(int a, int n, int sum)
{
	if(a > n)
	{
		cout<<sum<<endl;
		return ;
	}
	else
	{
		sum += a;
		Sum(++a, n, sum);
	}
}

int main()
{
	int ans, n;
	ans = 0;
	while (~scanf("%d", &n))
	{
		Sum(1, n, 0);
		cout<<endl;
	}
	return 0;
}