```cpp
using namespace std;
```
or
```cpp
std::cin >> n;
```
by lym12321 @ 2022-09-26 14:14:14
哦，原来这里没写
by HY_luogugu @ 2022-09-26 14:25:07
@[HYzhangshengyi](/user/377044) 我也是$HY$的$AvA$
by AC_CSP @ 2022-09-26 14:26:26