function place(curSlot)
  if turtle.getItemCount(curSlot) == 0 then
    for curSlot=curSlot,16 do
      if turtle.getItemCount(curSlot) > 0 then
        break
      end
    end
  end
  turtle.place()

  return curSlot
end

function checkFuel(curSlot)
  if turtle.getFuelLevel() < 1 then
    turtle.select(1)
    turtle.refuel(1)
    turtle.select(curSlot)
  end
end

function down(curSlot)
  checkFuel(curSlot)
  return turtle.down()
end

function up(curSlot)
  checkFuel(curSlot)
  return turtle.up()
end

local depth = 0

local curSlot = 2
turtle.select(2)

turtle.digDown()
while turtle.down() do
  for turn=1,4 do
    curSlot = place(curSlot)
    turtle.turnRight()
  end
  turtle.digDown()
  depth = depth + 1
end

for u = 1,depth do
  up()
end