foo.cc: In function 'int main()':
foo.cc:31:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   31 |   scanf("%d%d",&n,&m);
      |   ~~~~~^~~~~~~~~~~~~~
foo.cc:33:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   33 |    scanf("%d%d",&a,&b);
      |    ~~~~~^~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务