input: Write a function to find the nth Fibonacci number. If n is less than 0, it should print "Incorrect input" and return. If n is 0 or 1, it should return n. Otherwise, it should return the sum of the (n-1)th and (n-2)th Fibonacci numbers.
  def Fibonacci(n): 
      if n<0: 
          print("Incorrect input") 
      elif 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(-1) is None  # The function should print "Incorrect input" and return None
output: def Fibonacci(n): 
      if n<0: 
          print("Incorrect input") 
      elif n==0: 
          return 0
      elif n==1: 
          return 1
      else: 
          return Fibonacci(n-1)+Fibonacci(n-2)