#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <stdio.h>
#include <cstring>
#include <queue>
#include <stack>
#include <functional>
using namespace std;
#define Would
#define you


int main() {
	int n;
	cin >> n;
	cout << ((1 + n)*n) / 2 << endl;
}