foo.cc: In function 'int main()':
foo.cc:56:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf ("%d%d" , &n , &m);
  ~~~~~~^~~~~~~~~~~~~~~~~~
foo.cc:60:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf ("%d%d%d" , &a , &b , &c);
   ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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