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......