input: Write a function to compute the nth Fibonacci number. If the input n is less than 0, return an error message. If n is 0 or 1, return the respective Fibonacci number directly. For any other value of n, recursively compute the nth Fibonacci number by summing the two preceding Fibonacci numbers.
  def Fibonacci(n): 
      if n<0: 
          return "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)=="Incorrect input"
output: def Fibonacci(n): 
      if n<0: 
          return "Incorrect input" 
      elif n==0: 
          return 0
      elif n==1: 
          return 1
      else: 
          return Fibonacci(n-1)+Fibonacci(n-2)