using System;

class Program
{

    static void Main()
    {
        
        int N = int.Parse(Console.ReadLine());

        int sum = 0;

        if (1 <= N & N <= 100)
        {
            for (int i  = 0; i <= N; i++)
            {
                sum = sum + i;
            }
        }

        Console.Write(sum);
    }

}