input: Write a function to calculate the average of a list of positive integers and output the result. If the list is empty, return 0.
  assert average_of_positive_integers([1, 5, 6, 7, 8]) == 5.4
  assert average_of_positive_integers([3, 4, 5]) == 4.0
  assert average_of_positive_integers([10]) == 10.0
  assert average_of_positive_integers([]) == 0
  assert average_of_positive_integers([1, 2, 3, 4, 5]) == 3.0
output: def average_of_positive_integers(lst):
      if not lst:
          return 0
      return sum(lst) / len(lst)