using System;
using System.IO;
class Start
{
    static void Main()
    {
        var a = int.Parse(Console.ReadLine());
        Cs.WriteLine((a + 1) * a / 2);
        Cs.Flush();
    }
    static StreamWriter Cs = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
    static void Swap<T>(ref T a, ref T b) { T c = a; a = b; b = c; }
}