Minecart Builder Simple

local dist = 0
local pos = 0
local endDist = 0

print("End Distance:")
endDist = tonumber(read())

while dist < endDist do
	turtle.select(1)
	if turtle.getItemCount(1) == 0 then
		turtle.select(5)
		if turtle.getItemCount(5) == 0 then
			turtle.select(6)
			if turtle.getItemCount(6) == 0 then
				dist = endDist
				print("Out of track!")
			end
		end
	end
	for i=1, 20, 1 do
		turtle.forward()
		turtle.placeDown()
		dist = dist + 1
	end
	turtle.forward()
	turtle.select(2)
	turtle.placeDown()
	turtle.turnRight()
	turtle.forward()
	turtle.down()
	turtle.select(3)
	turtle.placeDown()
	turtle.up()
	turtle.select(4)
	turtle.placeDown()
	turtle.back()
	turtle.turnLeft()
	dist = dist + 1
end