def fun(n):
#print(n)
if n == 1 or n==0:
return n
else:
return fun(n-1) + fun(n-2)
print(fun(8))
# 基本情况 n==1 or n==0 返回n
# 递归步骤 f(n) = f(n-1) + f(n-2)
# 1,3,5,7,9,11......