foo.cc: In function 'int main()':
foo.cc:26:15: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   26 |         scanf ("%d%d", &n, &m);
      |         ~~~~~~^~~~~~~~~~~~~~~~
foo.cc:29:23: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   29 |                 scanf ("%d", a + i);
      |                 ~~~~~~^~~~~~~~~~~~~