Simple Mining Turtle Tunnel

print("How long should I go forward for?")
length=tonumber(read())
current=0
oneBehind=-1

function DigFace()
	turtle.turnLeft()
	turtle.dig()
	turtle.digDown() turtle.down()
	turtle.dig()
	turtle.digDown() turtle.down()
	turtle.dig()
	turtle.turnRight() turtle.turnRight()
	turtle.dig() turtle.up()
	turtle.dig() turtle.up()
	turtle.dig()
	turtle.turnLeft()
end

while current<length do
	if oneBehind<current then DigFace() end
	turtle.dig()
	oneBehind=oneBehind+1
	if turtle.forward() then
		current=current+1
		oneBehind=current-1
	end
end

turtle.turnRight() turtle.turnRight()
while current>0 do
	turtle.forward()
	current=current-1
end
turtle.down() turtle.down()

for i=1,16 do
	turtle.select(i)
	turtle.dropDown()
end