using System;

class Square
{
	static void Main(String[] args)
	{
		int D = int.Parse(Console.ReadLine());

		int hd = D/2;

		if(hd < 2)
		{
			Console.WriteLine(0);
			return;
		}

		long max = 0;

		for(int x=1; x<=hd/2+1; x++)
		{
			int y = hd-x;
			if(max < x * y)
				max = x * y;
		}
		Console.WriteLine(max);

	}
}