input: Write a function to prompt the user to enter the value of radius and calculate the area of a circle. The function should print the calculated area of the circle. If the input radius is invalid, the function should return an error message.
  
  def calculate_circle_area():
      Pi = 3.14
      try:
          radius = float(input("Please enter the radius of the circle: "))
          if radius < 0:
              raise ValueError("Radius cannot be negative.")
          area = Pi * radius ** 2
          print("The area of the circle is:", area)
      except ValueError as e:
          print("Invalid input:", e)
  
  assert calculate_circle_area() # Input: 5, Output: The area of the circle is: 78.5
  assert calculate_circle_area() # Input: -5, Output: Invalid input: Radius cannot be negative.
output: def calculate_circle_area():
      Pi = 3.14
      try:
          radius = float(input("Please enter the radius of the circle: "))
          if radius < 0:
              raise ValueError("Radius cannot be negative.")
          area = Pi * radius ** 2
          print("The area of the circle is:", area)
      except ValueError as e:
          print("Invalid input:", e)