input: def understand_recursion():
      """ This program is to understand recursion in Python.
      Define a recursive function to calculate the factorial of a number.
      Calculate factorial of number 5 and print the result.
      >>> understand_recursion()
      Factorial of 5 is 120
      """
output:     def factorial(n):
          if n == 0 or n == 1:
              return 1
          else:
              return n * factorial(n - 1)
  
      result = factorial(5)
      print(f"Factorial of 5 is {result}")