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

namespace 競プロ
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = Console.ReadLine();
            int N = int.Parse(s);

            int sum = 0;
            for(int i = 1; i <= N; i++)
                sum += i;

            Console.WriteLine(sum.ToString());
        }
    }
}