input: def fibonacci(n): 
      a = 0
      b = 1
      if n < 0: 
          return "Incorrect input"
      elif n == 0: 
          return a 
      elif n == 1: 
          return b 
      else: 
          for i in range(2, n + 1): 
              c = a + b 
              a = b 
              b = c 
          return b 
  
  # Example test cases
  # Test Case 1
  # Input: 9
  # Expected Output: 34
  # Test Case 2
  # Input: 0
  # Expected Output: 0
  # Test Case 3
  # Input: 1
  # Expected Output: 1
  # Test Case 4
  # Input: -1
  # Expected Output: "Incorrect input"
  
  print(fibonacci(9))
output:     print(fibonacci(0))
      print(fibonacci(1))
      print(fibonacci(-1))