Sirius

using System;
using System.IO;

namespace ConsoleApp2
{
    class Program
    {

        static void Main(string[] args)
        {
            int frst, scnd, perimetr, cnt = 0;
            perimetr = int.Parse(Console.ReadLine());
            for (frst = 1; frst < perimetr / 2; frst++)
            {
                for (scnd = 1; scnd < perimetr / 2; scnd++)
                {
                    if (frst * 2 + scnd * 2 == perimetr)
                    {
                        cnt += 1;
                    }
                }
            }
            Console.WriteLine(cnt);

        }
    }
}