foo.cc: In function 'bool check()':
foo.cc:9:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    9 |  for(int i=0;i<m.size();i++)
      |              ~^~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:33:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   33 |  scanf("%d",&n);
      |  ~~~~~^~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务