Dig Circle

os.loadAPI("t")
local start = t.getPos()
write("Radius: ")
local radius = tonumber(read())
for i=-radius,radius do
for j=-radius,radius do
local k=(i%2==0 and j or -j)
if (start:toVector() - vector.new(i,start.y,k)):length()<(radius-0.5) then
while not t.goto(i,start.y,k) do sleep(20) turtle.dig() end
if turtle.detectDown() then
turtle.digDown()
end
if turtle.getItemCount(16)>0 then
turtle.placeDown()
for o=2,16 do
turtle.select(o)
turtle.dropDown()
end
while turtle.getFuelLevel()<1000 do
print("Fuel empty")
turtle.refuel()
sleep(120)
end
turtle.select(1)
turtle.digDown()
end
end
end
end
start()