local slot = 1
local function refuel()
        local fuelLevel = turtle.getFuelLevel()
        if fuelLevel == "unlimited" or fuelLevel > 0 then
                return
        end

        local function tryRefuel()
                for n=1,16 do
                        if turtle.getItemCount(n) > 0 then
                                turtle.select(n)
                                if turtle.refuel(1) then
                                        turtle.select(1)
                                        return true
                                end
                        end
                end
                turtle.select(1)
                return false
        end

        if not tryRefuel() then
                print( "Add more fuel to continue." )
                while not tryRefuel() do
                        sleep(1)
                end
                print( "Resuming branch mine..." )
        end
end

while true do
turtle.select(slot)
refuel()
turtle.digDown()
turtle.placeDown()
turtle.forward()
end