using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Vælg et tal: ");

        int gentagelser = Convert.ToInt32(Console.ReadLine());

        int sum = 0;

        while(gentagelser>=0)

        {

        sum+=gentagelser;

        gentagelser--;

        }

        Console.WriteLine(sum);

    }

}