input: Write a function to calculate the average of five numbers entered by the user. Return the average as a float.
  assert calculate_average([3, 4, 5, 6, 7])==5.0
  assert calculate_average([1, 1, 1, 1, 1])==1.0
  assert calculate_average([0, 0, 0, 0, 0])==0.0
  assert calculate_average([10, 20, 30, 40, 50])==30.0
  assert calculate_average([-1, -2, -3, -4, -5])==-3.0
output: def calculate_average(numbers):
      return sum(numbers) / len(numbers)