foo.cc: In function 'int main()':
foo.cc:4:21: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
    4 | #define In() freopen("in.in","r",stdin)
      |              ~~~~~~~^~~~~~~~~~~~~~~~~~~
foo.cc:48:1: note: in expansion of macro 'In'
   48 | In();
      | ^~
foo.cc:49:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   49 | scanf("%d%d",&n,&m);mem(head,-1);
      | ~~~~~^~~~~~~~~~~~~~
foo.cc:53:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   53 | scanf("%d%d",&u,&v);
      | ~~~~~^~~~~~~~~~~~~~

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