foo.cc: In function 'int main()':
foo.cc:121:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d",&N,&M);
  ~~~~~^~~~~~~~~~~~~~
foo.cc:124:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d",&poi[i].x,&poi[i].y);
   ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:130:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d",&a,&b);
   ~~~~~^~~~~~~~~~~~~~

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