#include <iostream>
using namespace std;

int main() {
	
	long n = 0;
	long sum = 0;
	cin >> n;
	//循环相加
	for (int i = 1; i <= n; i++)
	{
		sum += i;
	}
	//打印结果
	cout << sum;
	system("pause");
	return 0;
 }