function deliver()
    if turtle.suck() == true then
        turtle.back()
        turtle.back()
        turtle.back()
        turtle.back()
        turtle.up()
        turtle.turnRight()
        turtle.drop()
    else
        deliver()
    end
end

function returnToChest()
    turtle.turnLeft()
    turtle.down()
    turtle.forward()
    turtle.forward()
    turtle.forward()
    turtle.forward()
end

function refuel()
    local movesLeft = turtle.getFuelLevel()
    if movesLeft<20 then
        turtle.select(2)
        turtle.refuel()
        turtle.select(1)
    end
end

function main()
    while true do
        refuel()
        deliver()
        returnToChest()
    end
end

main()