这题不能用动规吧，$n=5\times10^4$ 啊。
by zzq_666 @ 2023-08-02 18:36:29
@[114514tzy](/user/711322)
by zzq_666 @ 2023-08-02 18:36:34
@[zzq_666](/user/571841) 谢谢提醒，我自己再改一会
by __Misaka_Mikoto_ @ 2023-08-02 18:57:39