def largest_digit_helper(n, l_n):
	"""
	The function returns the largest digit in the integer.
	:param n: int.
	:param l_n: int, the largest digit.
	"""
	if n < 10:
		if n > l_n:
			l_n = n
		return l_n
	else:
		k = n % 10     # get units digit
		if k > l_n:    # get largest digit
			l_n = k
		n //= 10       # divide by 10
		return largest_digit_helper(n, l_n)