foo.cc: In function 'int main()':
foo.cc:34:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   34 |  freopen("city.in","r",stdin);
      |  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~
foo.cc:35:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   35 |  freopen("city.out","w",stdout);
      |  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
foo.cc:36:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   36 |  scanf("%d",&n);
      |  ~~~~~^~~~~~~~~
foo.cc:39:12: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   39 |       scanf("%d",&a[i][j]);
      |       ~~~~~^~~~~~~~~~~~~~~

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