input: Write a function to calculate the Fibonacci numbers up to a given number 'n'. The function should return the Fibonacci number at the position 'n'. If 'n' is 0, return 0. If 'n' is 1, return 1. For any other value of 'n', return the sum of the Fibonacci numbers at positions 'n-1' and 'n-2'.
  
  def Fibonacci(n): 
      if n==0: 
          return 0
      elif n==1: 
          return 1
      else: 
          return Fibonacci(n-1) + Fibonacci(n-2)
  
  assert Fibonacci(0) == 0
  assert Fibonacci(1) == 1
  assert Fibonacci(5) == 5
  assert Fibonacci(10) == 55
  assert Fibonacci(20) == 6765
output: def Fibonacci(n): 
      if n==0: 
          return 0
      elif n==1: 
          return 1
      else: 
          return Fibonacci(n-1) + Fibonacci(n-2)