class Integer
  def combination(k)
    return 0 if k < 0
    self.factorial/(k.factorial*(self-k).factorial)
  end

  def permutation(k)
    self.factorial/(self-k).factorial
  end

  def factorial
    return 1 if self == 0
    (1..self).inject(:*)
  end
end

class Yukicoder
  def initialize
    n = gets.to_i

    answer = 0.0

    1.upto(n) do |i|
      if i == 1
        answer += 1.0
      else
        size = i.combination(2)
        answer += 2 * Rational(1, i)

        [*(1..i-1)].combination(2) do |list|
          answer += Rational(list[0]*list[1], size)
        end
      end
    end

    puts answer
  end
end

Yukicoder.new