args = {...}
length = args[1]

function checkfuel()
	if turtle.getFuelLevel() <= 4 then
		turtle.select(16)
		turtle.refuel(1)
		turtle.select(1)
	end
end

function dig()
	while turtle.detect() do
		turtle.dig()
		os.sleep(.5)
	end
end

function digUp()
	while turtle.detectUp() do
		turtle.digUp()
		os.sleep(.5)
	end
end

function forward()
	checkfuel()
	while turtle.forward() == false do
		dig()
		turtle.attack()
		checkfuel()
		os.sleep(.5)
	end
	digUp()
	if turtle.detectDown() == false then
		turtle.placeDown()
	end
end

function tunnel(x)
	for i=1,x do
		forward()
		if i % 12 == 0 then
			turtle.turnLeft()
			turtle.turnLeft()
			turtle.select(15)
			turtle.place()
			turtle.select(1)
			turtle.turnLeft()
			turtle.turnLeft()
		end
	end
end

tunnel(length)