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