foo.cc:4:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
    4 | main()
      |      ^
foo.cc: In function 'int main()':
foo.cc:9:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    9 | scanf("%d",&n);
      | ~~~~~^~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务