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


namespace Пример
{

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

            int sum = 0;
            if (num<10000&&num>-10000)
            {


                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);
        }


    }

}