input:                         
  def Fibonacci(n): 
      if n==0: 
          return 0
      if n==1: 
          return 1
      else: 
          return Fibonacci(n-1)+Fibonacci(n-2)
  
  """
  Calculate the Fibonacci numbers up to a given number n.
  >>> Fibonacci(0)
  0
  >>> Fibonacci(1)
  1
  >>> Fibonacci(5)
  5
  """
output:     if n > 1:
          a, b = 0, 1
          for _ in range(2, n + 1):
              a, b = b, a + b
          return b