for i = 1, 16, 1 do
  for i = 1, 15, 1 do
    if turtle.detectDown() then
      turtle.digDown()
    end
    turtle.forward()
  end
  if i ~= 15 then
    if i % 2 == 0 then
      turtle.turnLeft()
      if turtle.detectDown() then
        turtle.digDown()
      end
      turtle.forward()
      turtle.turnLeft()
    else
      turtle.turnRight()
      if turtle.detectDown() then
        turtle.digDown()
      end
      turtle.forward()
      turtle.turnRight()
    end
  end
end
