using System;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            int sum = 0;
            String N = Console.ReadLine();
            int n = int.Parse(N);
            for (int i = 1; i <= n; i++)
            {
                sum += i;
            }
            Console.WriteLine(sum);
        }
    }
}