Submission #50640033

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class LastNSum
  def initialize n
    @n = n
    @sum =
    @first =
    @last = 0
    @values = [0]*n
  end
  attr_reader :sum
  def << value
    if @first == @last
      @sum -= @values[@first]
      @first = (@first+1)%@n
    end
    @sum += @values[@last] = value
    @last = (@last+1)%@n
  end
end
 
 
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class LastNSum
	def initialize n
		@n = n
		@sum =
		@first =
		@last = 0
		@values = [0]*n
	end

	attr_reader :sum

	def << value
		if @first == @last
			@sum -= @values[@first]
			@first = (@first+1)%@n
		end
		@sum += @values[@last] = value
		@last = (@last+1)%@n
	end
end

N,L,D = gets.split.map(&:to_i)

*P = 1.0
s = LastNSum.new D
s<<P[-1]
1.upto(N){|y|
	P<<s.sum/D
	s<<(y<L ? P[-1] : 0)
}

勝つ = nil
振って勝つ = LastNSum.new D
振らずに勝つ = 1.0
N.downto(0){|y|
	振らずに勝つ -= P[y] if L<=y
	勝つ = [振らずに勝つ,振って勝つ.sum/D].max
	振って勝つ<<勝つ
}

p 勝つ

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Judge Result