/* package whatever; // don't place package name! */

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

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		int sum = 0;
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		
		for(int i=0;i<=n;i++){
			sum +=i;
		}
		
		System.out.println(sum);
	}
}