input: 
  def calculate_average(nums: List[int]) -> float:
      """ Calculate the average of a list of five numbers.
      >>> calculate_average([1, 2, 3, 4, 5])
      3.0
      >>> calculate_average([10, 20, 30, 40, 50])
      30.0
      """
  
output:     if len(nums) != 5:
          raise ValueError("The list must contain exactly five numbers.")
      return sum(nums) / 5