input: Write a function to calculate the average of a list of positive integers and output the result. The function should take a list of positive integers as input and return the average of the numbers in the list. If the list is empty, return 0.
  assert calculate_average([1, 5, 6, 7, 8])==5.4
  assert calculate_average([10, 20, 30, 40, 50])==30.0
  assert calculate_average([])==0
  assert calculate_average([2, 4, 6, 8])==5.0
output: def calculate_average(numbers):
      if not numbers:
          return 0
      return sum(numbers) / len(numbers)