foo.cc: In function 'int main()':
foo.cc:11:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf ("%d%d%d%d" , &n , &m , &s , &t);
  ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:19:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf ("%d%d%d" , &a , &b , &w);
   ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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