foo.cc: In function 'int main()':
foo.cc:25:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
     freopen("666.in","r",stdin);
     ~~~~~~~^~~~~~~~~~~~~~~~~~~~
foo.cc:26:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
     freopen("666.out","w",stdout);
     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
foo.cc:27:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d",&n,&k);
  ~~~~~^~~~~~~~~~~~~~
foo.cc:29:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a[i]);
   ~~~~~^~~~~~~~~~~~

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