input: Write a function to compute the nth Fibonacci number. If the input n is less than 0, print "Incorrect input". If n is 0 or 1, return the value of n. Otherwise, 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(7)==13
  assert Fibonacci(-3)=="Incorrect input"
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)