package app;

import java.util.*;

public class App {
    public static void main(String[] args) throws Exception {
        Scanner scan = new Scanner(System.in);
        String str = scan.nextLine();

        int n = Integer.parseInt(str);
        int sum = 0;

        for(int i=1; i<=n; i++) {
            sum += i;
        }

        System.out.println(sum);
        scan.close();

    }
}