input: def divisibleBy3(numbers: List[int]) -> int:
      """
      Calculate the sum of all elements in a list of integers that are divisible by 3.
      >>> divisibleBy3([4, 6, 17, 24, 5, 9])
      42
      >>> divisibleBy3([1, 2, 3, 4, 5])
      3
      """
output:     total = 0
      for num in numbers:
          if num % 3 == 0:
              total += num
      return total