foo.c: In function 'SetUnion':
foo.c:24:21: warning: unused variable 'k' [-Wunused-variable]
     int i, j, c[N], k = 0;
                     ^
foo.c: In function 'main':
foo.c:35:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d%d", &m, &n, &p);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:37:9: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d", &a[i]);
         ^~~~~~~~~~~~~~~~~~
foo.c:39:9: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d", &b[i]);
         ^~~~~~~~~~~~~~~~~~
foo.c:41:9: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d", &c[i]);
         ^~~~~~~~~~~~~~~~~~

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