foo.c: In function 'main':
foo.c:6:18: warning: unused variable 'k' [-Wunused-variable]
  int na, nb, nc, k, i;
                  ^
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d %d", &na, &nb, &nc);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:10:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &a[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:12:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &b[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:14:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &c[i]);
   ^~~~~~~~~~~~~~~~~~

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