foo.cc: In function 'int main()':
foo.cc:29:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     int n; scanf("%d",&n);
            ~~~~~^~~~~~~~~
foo.cc:32:20: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
      int x,y; scanf("%d%d",&x,&y);
               ~~~~~^~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。