input: def calculate_average(numbers: List[int]) -> float:
      """ Calculate the average of a list of positive integers.
      >>> calculate_average([1, 5, 6, 7, 8])
      5.4
      >>> calculate_average([10, 20, 30, 40])
      25.0
      """
output:     if not numbers:
          return 0.0
      total = sum(numbers)
      count = len(numbers)
      return total / count