foo.cc: In function 'int main()':
foo.cc:5:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("match.in","r",stdin);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
foo.cc:6:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("match.out","w",stdout);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

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