マイクラチュートリアル2-2 ピラミッド建築

i = 3
j = i
s = 1
turtle.up()
turtle.select(s)

for n = 1, i do
  for n = 1, 4 do
    for n = 1, j * 2 do
      if turtle.getItemCount() == 0 then
        s = s + 1
        turtle.select(s)
      end
      turtle.placeDown()
      turtle.forward()
    end
    turtle.turnLeft()
  end
  j = j - 1
  turtle.turnRight()
  turtle.back()
  turtle.turnLeft()
  turtle.forward()
  turtle.up()
end
turtle.placeDown()