tBedrockLadder

local function detectAndPlace()
    if turtle.detect() == false then
        turtle.select(1)
        turtle.place(1)
    end
end

local function checkSides()
    detectAndPlace()
    turtle.turnLeft()
    detectAndPlace()
    turtle.turnLeft()
    detectAndPlace()
    turtle.turnLeft()
    detectAndPlace()
    turtle.turnLeft()
end

local function placeLadder()
    if turtle.detect() then
        turtle.dig()
        turtle.select(16)
        turtle.place(1)
    end
end

local times = 0
term.write("How deep:")
times = read()
for j = 1, times do
    turtle.digDown()
    turtle.down()
    checkSides()
end
for k = 1, times do
    placeLadder()
    turtle.up()
end