input: 
  from typing import List
  
  def find_max(numbers: List[int]) -> 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
      """
  
output:     if not numbers:
          return -1
      max_num = numbers[0]
      for num in numbers:
          if num > max_num:
              max_num = num
      return max_num