ural1068

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;


class Program
{
    static void Main(string[] args)
    {
        p1001 p = new p1001();
    }
}

class RTIO
{
    static string bufferStr = "";
    public static int GetInt()
    {
        if (bufferStr.Length == 0)
        {
            bufferStr = Console.ReadLine();
        }
        int index = bufferStr.IndexOf(' ');
        if (index < 0) index = bufferStr.Length;

        int res = int.Parse(bufferStr.Substring(0, index));
        if (index != bufferStr.Length)
        {
            bufferStr = bufferStr.Remove(0, index + 1);
        }
        return res;
    }
}

class p1001
{
    public p1001()
    {
        int x = RTIO.GetInt();
        Console.WriteLine((x + 1) * (Math.Abs(x - 1) + 1) / 2);
    }
}