foo.c: In function 'main':
foo.c:22:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   22 |  scanf("%d %d %d", &n1, &n2, &n3);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:24:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   24 |   scanf("%d", &a1[i]);
      |   ^~~~~~~~~~~~~~~~~~~
foo.c:26:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   26 |   scanf("%d", &a2[i]);
      |   ^~~~~~~~~~~~~~~~~~~
foo.c:28:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   28 |   scanf("%d", &a3[i]);
      |   ^~~~~~~~~~~~~~~~~~~

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