foo.cc: In function 'int main()':
foo.cc:36:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   36 |  scanf("%d%d", &n, &m);
      |  ~~~~~^~~~~~~~~~~~~~~~
foo.cc:40:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   40 |   scanf("%d%d%d%d", &x, &y, &c, &d), add(x, y, c, d), add(y, x, c, d);
      |   ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:42:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   42 |  scanf("%d%d%d", &a, &b, &k);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~~~~

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