input: 
  def find_max(numbers: list) -> int:
      """Find the maximum number from a list of non-negative integers.
      >>> find_max([1, 3, 12, 5, 8, 10])
      12
      >>> find_max([0, 0, 0, 0])
      0
      >>> find_max([4, 7, 1, 9, 2, 8])
      9
      """
      max_num = 0
      for num in numbers:
          if num > max_num:
              max_num = num
      return max_num
  
output:     max_num = 0
      for num in numbers:
          if num > max_num:
              max_num = num
      return max_num