foo.cc: In function 'int main()':
foo.cc:23:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d", &n, &m);
  ~~~~~^~~~~~~~~~~~~~~~
foo.cc:38:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &k);
  ~~~~~^~~~~~~~~~
foo.cc:42:8: 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。