foo.cc: In function 'int main()':
foo.cc:18:15: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  int n,m;scanf("%d%d",&n,&m);
          ~~~~~^~~~~~~~~~~~~~
foo.cc:24:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%d",&a[j][i]);
    ~~~~~^~~~~~~~~~~~~~~

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