input: from typing import List
  
  
  def max_of_three(numbers: List[int]) -> int:
      """ Find the maximum of three numbers.
      >>> max_of_three([3, 4, 5])
      5
      >>> max_of_three([10, 2, 7])
      10
      """
output:     if len(numbers) != 3:
          raise ValueError("The list must contain exactly three numbers.")
      return max(numbers)