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

public class Main {
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		// 入力
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		
		// 計算
		int result = (N+1 + 1) * (N+1) / 2;
		
		// 出力
		System.out.println(result);
	}
}