求这个怎么按下门的方法写👄

有帮助能点个采纳吗，谢谢~

n=eval(input('n='))
Sn=100.0
#Function-fun-start
def fun(n,Sn):
    total=Sn
    for i in range(1,n):
         total+=Sn
         Sn/=2
    return total

Sn=fun(n,Sn)
#Function-fun-end

print(Sn)