foo.cc: In function 'int main()':
foo.cc:20:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d", &n1, &n2, &n3);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:23:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &a1[i]);
   ~~~~~^~~~~~~~~~~~~~
foo.cc:27:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &a2[i]);
   ~~~~~^~~~~~~~~~~~~~
foo.cc:31:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &a3[i]);
   ~~~~~^~~~~~~~~~~~~~

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