gravedigger

function clear()
 term.clear()
 term.setCursorPos(1,1)
end

function fuel()
 turtle.select(2)
 turtle.refuel()
 turtle.select(1)
end

function ladder()
 turtle.select(1)
 turtle.place()
end

function pillar()
 turtle.down()
 turtle.forward()
 turtle.detect()
 turtle.select(3)
 turtle.place()
 turtle.back()
 turtle.select(1)
 turtle.place()
end

write("Depth: ")
local var = tonumber(read())
fuel()
 for i = 1, var do
  if turtle.detectDown() then
   turtle.digDown()
   turtle.down()
   turtle.dig()
   ladder()
  else
   pillar()
  end
 end