foo.cc: In function 'void in()':
foo.cc:18:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   18 | scanf("%d%d", &n, &m);
      | ~~~~~^~~~~~~~~~~~~~~~
foo.cc:21:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   21 | scanf("%d%d", &a, &b);
      | ~~~~~^~~~~~~~~~~~~~~~

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