Spiral Staircase Computercraft

local arg = {...}

function step()
  turtle.digUp()
  turtle.up()
  turtle.digUp()
  turtle.dig()
  turtle.forward()
  checkAndPlace()
  turtle.digUp()
  turtle.up()
  turtle.digUp()
  turtle.dig()
  turtle.forward()
  checkAndPlace()
  turtle.digUp()
  turtle.turnLeft()
end

function checkAndPlace()
  if(not turtle.detectDown()) then
    turtle.placeDown()
end


for  i = 1, tonumber(arg[1]) do
  step()
end