foo.c: In function 'main':
foo.c:6:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d", &n1, &n2, &n3);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:8:4: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   {scanf("%d", &a1[i]);}
    ^~~~~~~~~~~~~~~~~~~
foo.c:10:4: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   {scanf("%d", &a2[j]);}
    ^~~~~~~~~~~~~~~~~~~
foo.c:12:4: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   {scanf("%d", &a3[k]);}
    ^~~~~~~~~~~~~~~~~~~

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