1 def fabm(n):
 2     if n < 1:
 3         print(‘输入不能小于1‘)
 4         return -1
 5 
 6     if n == 1 or n == 2:
 7         return 1
 8     else:
 9         return fabm(n-1) + fabm(n-2)
10 
11 result = fabm(19)
12 if result != -1:
13     print(‘结果是%d‘ % result)