1  def fibonacci(n):
 2      """Calculate the nth Fibonacci number."""
 3      if n <= 1:
 4          return n
 5      return fibonacci(n-1) + fibonacci(n-2)
 6  
 7  def factorial(n):
 8      """Calculate factorial of n."""
 9      if n == 0:
10          return 1
11      return n * factorial(n-1)