using System;

public class Program

{

     static int PrintNumbers(int n) {

        if (n == 1){

            return 1;

        } 

        else 

            return PrintNumbers(n-1) + n;

    }

    public static void Main(string[] args)

    {

        int n, sum;

        n = int.Parse(Console.ReadLine());

        sum = PrintNumbers(n);

        Console.WriteLine("sum="+sum);      

    }

}