import java.util.*;
import java.lang.*;
import java.io.*;

// The main method must be in a class named "Main".
class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        int m = 0;
        for(int i = 0;i <= n;i++){
            m+=i;
        }
        System.out.println(m);
    }
}