import java.util.Scanner;

class Wandbox
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        int b = 0;
        
        for(int i=0;i<a;i++) {
             b += i+1;
        }

        System.out.println(b);
    }
}