BOX = [1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
draws = []

100_000.times do
    prev = 0
    draws_num = 0

    20.times do
        ball = BOX.sample
        draws_num += 1 if ball.zero? && prev.nonzero?
        prev = ball
    end

    draws_num += 1 if prev.nonzero?
    draws.push draws_num
end

puts draws.sum.to_f / draws.size