class Calc0080
  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @d = args.shift.first.to_i
  end

  def run
    d2 = @d / 2
    (1..(d2 / 2)).map { |k| k * (d2 - k) }.max || 0
  end
end

puts Calc0080.new(STDIN.readlines).run if __FILE__ == $0