class Calc0111
  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @l = args.shift.first.to_i
  end

  def run
    ((@l - 1) / 2) ** 2
  end
end

puts Calc0111.new(STDIN.readlines).run if __FILE__ == $0