using System;

public class Program

{

    public static void Main()

    {

        int n,i,sum=0;

        Console.WriteLine("n=");

        n=Convert.ToInt32(Console.ReadLine());

        for(i=1;i<=n;i++)

        {

            sum=sum+i;

        }

        Console.WriteLine("sum={0}",sum);

    }

}