#include <iostream>
using namespace std;
short n;
int main()
{
	cin >> n;
	long long sum;
	for (int i = 1;i <= n;i++)
		sum += i;
	cout << sum - 1;
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
#define LL long long
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
long long  n , ans;
int main()
{
	cin >> n;
	for ( long long i = 1 ; i <= n ; i++ )
	{
		ans += i;
	}
	cout << ans;
	return 0;
}
//菜鸟驿站
//老六专属

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