func_code: def fibonacci(n):
      i = 0
      while i < n:
          if n[i] == 0:
              return i
          i += 1
      return c
      c = i + 1
  
  
  def index(str, letter):
      i = 0
      while i < len(str):
          if str[i] == letter:
              return i
          i += 1
      return -1