foo.cc: In function 'int main()':
foo.cc:32:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0; i<graph[now].size(); i++) {
                ~^~~~~~~~~~~~~~~~~~
foo.cc:13:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d",&n,&m);
  ~~~~~^~~~~~~~~~~~~~~
foo.cc:16:8: 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 进行评测(github.com/hydro-dev/HydroJudge)

{"receive":"2020-07-11T13:31:03.870Z","handle":"2020-07-11T13:31:03.870Z","cache_start":"2020-07-11T13:31:03.877Z","read_cases":"2020-07-11T13:31:04.007Z","judge":"2020-07-11T13:31:04.008Z","done":"2020-07-11T13:31:04.531Z"}