foo.c: In function 'main':
foo.c:6:10: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  int n1; scanf("%d",&n1);
          ^~~~~~~~~~~~~~~
foo.c:7:10: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  int n2; scanf("%d",&n2);
          ^~~~~~~~~~~~~~~
foo.c:8:10: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  int n3; scanf("%d",&n3);
          ^~~~~~~~~~~~~~~
foo.c:11:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a1[i]); 
   ^~~~~~~~~~~~~~~~~~
foo.c:15:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a2[i]); 
   ^~~~~~~~~~~~~~~~~~
foo.c:19:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a3[i]); 
   ^~~~~~~~~~~~~~~~~~

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