input: Write a function to generate the nth number in the Fibonacci sequence. The function should return the nth Fibonacci number. If the input is less than 0, the function should print "Incorrect input".
  def fibonacci(n): 
      a = 0
      b = 1
      if n < 0: 
          print("Incorrect input") 
      elif n == 0: 
          return a 
      elif n == 1: 
          return b 
      else: 
          for i in range(2,n): 
              c = a + b 
              a = b 
              b = c 
          return b 
  
  # Test cases
  assert fibonacci(9) == 21
  assert fibonacci(0) == 0
  assert fibonacci(1) == 1
  assert fibonacci(5) == 3
  assert fibonacci(10) == 34
output: def fibonacci(n): 
      a = 0
      b = 1
      if n < 0: 
          print("Incorrect input") 
      elif n == 0: 
          return a 
      elif n == 1: 
          return b 
      else: 
          for i in range(2,n): 
              c = a + b 
              a = b 
              b = c 
          return b