local i = 0
while i < 16 do
 turtle.dig()
 turtle.forward()
 turtle.digUp()
 i = i +1
end
i = 0
turtle.turnLeft()
while i < 16 do
 turtle.dig()
 turtle.forward()
 turtle.digUp()
 i = i +1
 if i == 5 then
  turtle.select(16)
  turtle.placeUp()
 end
 if i == 10 then
  turtle.select(16)
  turtle.placeUp()
 end
 if i == 15 then
  turtle.select(16)
  turtle.placeUp()
 end
end