using System;

namespace ConsoleApp10
{
    class Program
    {
        static void Main(string[] args)
        {
            int number = 0;
            int N = int.Parse(Console.ReadLine());

            for(int i=1;i<=N;++i)
            {
                number += i;
            }
            Console.WriteLine(number);
            Console.ReadLine();
        }
    }
}