input: from typing import List
  
  
  def fibonacci(n: int) -> int:
      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
  print(fibonacci(9))  # Expected output: 21
output:     for i in range(2, n + 1):
          c = a + b
          a = b
          b = c
      return b