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

namespace YukiCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            long na = long.Parse(Console.ReadLine());
            long nn = (na - 1) / 2;
            Console.WriteLine(nn * nn);
            Console.ReadLine();
        }
    }
}