foo.c: In function 'main':
foo.c:26:21: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  int n1, n2, n3, i; scanf("%d%d%d", &n1, &n2, &n3);
                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:29:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &a1_2[i]);
   ^~~~~~~~~~~~~~~~~~~~~
foo.c:33:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &a2[i]);
   ^~~~~~~~~~~~~~~~~~~
foo.c:35:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &a3[i]);
   ^~~~~~~~~~~~~~~~~~~

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