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

class Program
{
    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        string wkStr;
        while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        int D = int.Parse(InputList[0]);

        int MaxMenseki = 0;
        for (int X = 1; X * 2 <= D; X++) {
            for (int Y = X; X * 2 + Y * 2 <= D; Y++) {
                int Memseki = X * Y;
                if (MaxMenseki < Memseki)
                    MaxMenseki = Memseki;
            }
        }
        Console.WriteLine(MaxMenseki);
    }
}