input: Write a function to determine if it is possible to get a number where the sum of its digits equals the original number by adding or subtracting each digit individually. If it is possible return True else return False. If the given number is less than 10 then return True.
  assert digit_sum_equals_number(18)==True
  assert digit_sum_equals_number(528)==True
  assert digit_sum_equals_number(193)==False
  assert digit_sum_equals_number(767)==False
  assert digit_sum_equals_number(5)==True
output: def digit_sum_equals_number(n):
      if n < 10:
          return True
      digits = [int(d) for d in str(n)]
      def can_sum(target, digits):
          if target == 0:
              return True
          if not digits:
              return False
          return can_sum(target - digits[0], digits[1:]) or can_sum(target + digits[0], digits[1:])
      return can_sum(0, digits)