using System;
using System.Collections.Generic;
using System.Linq;
using static System.Math;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            y();
        }

        static void y()
        {
            var sum = 0;
            for (int i = 1; i <= int.Parse(Console.ReadLine()); i++)
            {
                sum += i;
            }
            Console.WriteLine(sum);
        }

    }
}