foo.cc: In function 'int main()':
foo.cc:27:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d",&m,&n);
  ~~~~~^~~~~~~~~~~~~~~
foo.cc:30:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%d",&b[i][j]);
    ~~~~~^~~~~~~~~~~~~~~

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