place sand

local emptyFlag =false
local bkslot = 2
while 1 do
    -- check fuel
    if(turtle.getFuelLevel() < 100) then
        turtle.select(1)
        turtle.refuel(1)
    end
    -- check space
    turtle.select(bkslot)
    if(emptyFlag == false) then
        while (turtle.getItemCount() == 0) do
            bkslot = bkslot + 1
            if(turtle.getItemCount(2) ~= 0) then
                bkslot = 2
                break
            end
            if(bkslot > 16) then
                exit()
            end
            turtle.select(bkslot)
        end
    end
    -- check block
    if(turtle.detectDown()) then
        select(10)
    end
    turtle.place()
    turtle.placeDown()
end