mine

function main()
  upmode=0
  downmode=1
  turtle.select(2)
  turtle.placeUp()
  turtle.select(1)
  print(turtle.getFuelLevel())
  while true do
    if turtle.getFuelLevel()==0 then
      turtle.refuel()
    end
    if downmode==1 then
      turtle.digDown()
      if turtle.detectDown()==true then
        upmode=1
        downmode=0
      end
      turtle.down()
    end
    if upmode==1 then
      turtle.up()
      if turtle.detectUp()==true then
        turtle.digUp()
        upmode=0
      end
    end
  end
end
main()