chop

c = 0

while true do

a = 0
b = 0

--refuel
  if turtle.getFuelLevel() < 20 then
    turtle.select(16)
    turtle.refuel(60)
  end

--code

  turtle.select(1)
  if turtle.compare() then
    turtle.dig()
    turtle.forward()
      while turtle.compareUp() do
        turtle.digUp()
        turtle.up()
        a = a + 1
      end
     while a > 0 do
       turtle.down()
       a = a - 1
     end
     turtle.back()
     turtle.select(15)
     turtle.place()

    if c < 2 then
      turtle.turnRight()
      for i=1,4 do
         turtle.forward()
      end
      turtle.turnLeft()
      c = c + 1
    else
      turtle.turnLeft()
      for i=1,8 do
        turtle.forward()
      end
      c = 0
      turtle.turnRight()
    end

  end --if

end