Stairs up

write("How many meters to go?: ")
z = read()
z = tonumber(z)
if z < 1 then
  print("No number given.")
  return
end

for lz = 1, z do
  turtle.dig()
  turtle.forward()
  if not turtle.detectDown() then
    turtle.placeDown()
  end
  turtle.digUp()
  turtle.up()
  turtle.digUp()
  turtle.up()
  turtle.digUp()
  turtle.placeUp()
  turtle.down()
end

for lz = 1, z do
  turtle.down()
  if lz < z then
    turtle.back()
  end
end