func_code: def fibonacci(n):
      if n == 0:
          return 0
      if n == 1:
          return 1
      else:
          fibN_2 = 0
          fibN_1 = 1
          i = 2
          while i <= n:
              fibN = fibN_2 + fibN_1
              fibN_2 = fibN_1
              fibN_1 = fibN
              i = i + 1
          return fibN