using System;

public class Program

{

    public static int mul(int multiply)

    {

        if (multiply == 1)

        {

            return 1;

        }

        else

        {

            return multiply + mul(multiply-1);

        }

    }

    public static void Main()

    {

        Console.Write("How many numbers: ");

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

        Console.WriteLine("Sum of the numbers are "+mul(multiply));

    }

}