input: Write a function to calculate the average of a list of positive integers and output the result.
  
  assert calculate_average([1, 5, 6, 7, 8])==5.4
  assert calculate_average([10, 20, 30, 40, 50])==30.0
  assert calculate_average([1, 2, 3, 4, 5])==3.0
  assert calculate_average([])==0.0
  assert calculate_average([7, 8, 9, 10, 11])==9.0
output: def calculate_average(numbers):
      if not numbers:
          return 0.0
      return sum(numbers) / len(numbers)