using System;

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

            for (long i = 0; i < n; i++)
            {
                long num = n * i - i * i + n;
                if (num > max) max = num;
            }

            Console.WriteLine(max);
        }
    }
}