foo.cc: In function 'int main()':
foo.cc:6:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf ("%d%d", &n, &m);
  ~~~~~~^~~~~~~~~~~~~~~~
foo.cc:7:28: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for (i=0; i<n; i++) scanf ("%d", &a[i]);
                      ~~~~~~^~~~~~~~~~~~~
foo.cc:8:28: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for (i=0; i<m; i++) scanf ("%d", &b[i]);
                      ~~~~~~^~~~~~~~~~~~~

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