function four1()
    turtle.turnright()
    turtle.forward()
    turtle.turnRight()
    while not turtle.detect() do
        turtle.forward()
    end
end

function flush()
    for i = 1, 16, 1 do
        turtle.select(i)
        turtle.dropDown()
    end
    turtle.select(1)
end

function four2()
    turtle.back()
    turtle.turnLeft()
    turtle.forward()
    turtle.forward()
    turtle.turnRight()
    turtle.forward()
end

function retour()
    turtle.back()
    turtle.turnRight()
    turtle.forward()
    turtle.forward()
    turtle.turnRight()
    while not turtle.detect() do
        turtle.forward()
    end
    turtle.turnRight()
end

while (1) do
    four1()
    flush()
    four2()
    flush()
    retour()
    sleep(180)
end