func_code: def fibonacci(n):
      fib = [0, 1, 1]
      for f in range(2, n):
          fib.append(fib[-1] + fib[-2])
      return fib[n]
  
  
  def index(str, letter):
      i = 0
      while i < len(str):
          if str[i] == letter:
              return i
          i += 1
      return -1