using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp21
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            int x = 0;
            for (int i = n; i != 0; --i)
            {
                x = x + i; ;

            }


            Console.WriteLine("{0}",x);
            Console.ReadLine();



        }
    }
}