using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Text;


namespace Пример
{

    class Programm
   {
         static void Main(string[] args)
        {
           int num= Convert.ToInt32( Console.ReadLine());

            int sum = 0;
            if (num > 0)
            {
                for (int i = 1; i <= num; i++)
                {
                    sum += i;
                }
            }
            else if (num < 0)
            {
                for (int i =num; i <=1; i++)
                {
                    sum += i;
                }
            }

            Console.WriteLine(sum);
        }


    }

}