local distance = 0

function mf()
    if turtle.getFuelLevel() < 1 then
      turtle.select(16)
      if turtle.refuel(0) then
            turtle.refuel(1)
      else
        error()
      end
    end
    while not turtle.forward() do
      if not turtle.dig() then
        turtle.attack()
      end
    end
end

function du()
    while turtle.detectUp(true) do
        turtle.digUp()
    end
end

function digStrip(length)
    local i = 0
    while i < length do
        mf()
        i = i + 1
    end
end

function lShape(length)
    digStrip(length)
    turtle.turnLeft()
    digStrip(length)
    turtle.turnLeft()
end

while true do
    lShape(distance)
    distance = distance + 1
end