foo.cc: In function 'int main()':
foo.cc:13:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d", &n, &m);
  ~~~~~^~~~~~~~~~~~~~~~
foo.cc:15:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &vn[i].id, &vn[i].num);
   ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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