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

namespace No480
{
    public class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            System.Console.WriteLine(NewMethod(n));
        }

        public static int NewMethod(int n)
        {
            int sum = (1 + n) * n / 2;

            return sum;
        }
    }
}