import java.io.*;
import java.util.*;
import java.util.Scanner;
public class Main{
	public static void main (String[] args)
	{
    Scanner sc = new Scanner(System.in);
    PrintWriter out = new PrintWriter(System.out);
    int i1=sc.nextInt();
	int j=0;
	for (int i = 0; i<i1+1;i++) {
		j=j+i;
	}
	out.println(j);
        out.flush();
	}
}