input: Write a function to find the nth Fibonacci number. If the input is less than 0, print "Incorrect input" and return None. If the input is 0, return 0. If the input is 1, return 1. Otherwise, return the sum of the two preceding 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) == 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)