def largest_product_in_a_series(number_string):
	"""
	Create a window of 13 characters that traverses the entire number and finds product for each window. Linear time complexity.
	"""
	left, right = 0, 13
	largest_product = 0
	while right < len(number_string):
		window = number_string[left:right]
		product = eval('*'.join(window))
		if product > largest_product:
			largest_product = product
		left += 1
		right += 1
	return largest_product