foo.cc: In function 'int main(int, char**)':
foo.cc:20:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d", &n1, &n2);
  ~~~~~^~~~~~~~~~~~~~~~~~~
foo.cc:21:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d", &m1, &m2);
  ~~~~~^~~~~~~~~~~~~~~~~~~

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