Computer Craft Mob Grinder

function grinder()
 while true do
  while turtle.getItemCount(1) < 64 do
   turtle.attackUp()
   turtle.suckUp()
   os.sleep(2)
  end
  if turtle.getItemCount(1) == 64 then
   turtle.select(1)
   turtle.drop(63)
   if turtle.getItemCount(2) < 0 then
    turtle.select(2)
    turtle.dropDown()
    if turtle.getItemCount(3) < 0 then
     turtle.select(3)
     turtle.dropDown()
     if turtle.getItemCount(4) < 0 then
      turtle.select(4)
      turtle.dropDown()
      if turtle.getItemCount(5) < 0 then
       turtle.select(5)
       turtle.dropDown()
       if turtle.getItemCount(6) < 0 then
        turtle.select(6)
        turtle.dropDown()
       end
      end
     end
    end
   end
  end
 end
end
grinder()