def inter_means(sequences)
  Enumerator.new do |y|
    last_inserted = nil
    sequences.lazy.each do |seq|
      first = true
      seq.lazy.each do |element|
        if first && last_inserted
          y << (element + last_inserted) / 2.0
          last_inserted = nil
        end
        first = false
        y << element
        last_inserted = element
      end
    end
  end
end
 
stdin_stream = Enumerator.new do |y|
  number = ""
  STDIN.each_char.lazy.each do |c|
  	print c # Показать порядок ввода и вычисления
    if c =~ /\d/
      number += c
    else
      y << number.to_i if number != ""
      number = ""
    end
  end
  y << number.to_i if number != ""
end
 
inputs = [
  [[], stdin_stream.lazy, [1]],
  # [[*1..5], [*3..6].reverse, [], [-3, -3, -3]],
  # [],
  # [[], [1, 2, 3], [], [-3, -2, -1], [], []]
]
 
inputs.each do |input|
  puts "  #{input.inspect}"
  puts "#{inter_means(input).each { |n| puts "<#{n}>" }}"
end
 
#   [[1, 2, 3, 4, 5], [6, 5, 4, 3], [], [-3, -3, -3]]
# => [1, 2, 3, 4, 5, 5.5, 6, 5, 4, 3, 0.0, -3, -3, -3]
#   []
# => []
#   [[], [], []]
# => []
#   [[], [1, 2, 3], [], [-3, -2, -1], [], []]
# => [1, 2, 3, 0.0, -3, -2, -1]

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