foo.cc: In function 'void prep()':
foo.cc:10:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   10 | scanf("%d",&n);
      | ~~~~~^~~~~~~~~
foo.cc:13:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   13 | scanf("%d",&B[forn]);
      | ~~~~~^~~~~~~~~~~~~~~

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