foo.cc: In function 'int main()':
foo.cc:30:6: warning: unused variable 't' [-Wunused-variable]
  int t;
      ^
foo.cc:28:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("p1456.in", "r", stdin);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:29:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
  ~~~~~^~~~~~~~~~
foo.cc:35:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%d", &edges[i][j]);
    ~~~~~^~~~~~~~~~~~~~~~~~~~

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