【python】迭代一列 斐波那契数列

 def fabm(n):
     if n < 1:
         print('输入不能小于1')
         return -1

     if n == 1 or n == 2:
         return 1
     else:
         return fabm(n-1) + fabm(n-2)

 result = fabm(19)
 if result != -1:
     print('结果是%d' % result)