foo.c: In function 'main':
foo.c:21:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ^~~~~~~~~~~~~~~
foo.c:23:9: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d", &a[i]);
         ^~~~~~~~~~~~~~~~~~
foo.c:24:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &k);
     ^~~~~~~~~~~~~~~

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