using System;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        int n = int.Parse(Console.ReadLine());
        int ans = 0;

        for (int i = 1; i <= n; i++)
        {
            ans += i;
        }

        Console.WriteLine(ans);
        Console.ReadLine();
    }
}