func_code: def fibonacci(n):
      a, b = 0, 1
      for i in range(n):
          a, b = b, a + b
      return a
  
  
  def index(str, letter, pos):
      i = str[0]
      pos = 1
      while i < len(str):
          if letter in str:
              letter_pos = i + 1
          i = i + 1
      return letter_pos