import turtle

def draw(length, depth):
   if depth == 0:
     turtle.forward(length)
   else:
     draw(length/3, depth-1)
     turtle.right(60)
     draw(length/3, depth-1)
     turtle.left(120)
     draw(length/3, depth-1)
     turtle.right(60)
     draw(length/3, depth-1)

draw(500, 4)