using System; using System.IO; using System.Linq; using System.Collections; using System.Collections.Generic; using System.Numerics; using System.Text; using System.Text.RegularExpressions; using System.Threading.Tasks; using static System.Math; using Int = System.Int64; using Debug = System.Diagnostics.Debug; class P { static void Main() { Console.WriteLine(Enumerable.Range(1, int.Parse(Console.ReadLine())).Sum()); } }