foo.c:3:6: warning: return type of 'main' is not 'int' [-Wmain]
 void main()
      ^~~~
foo.c: In function 'main':
foo.c:6:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d%d",&n1,&n2,&n3);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:8:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a1[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:10:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a2[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:12:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a3[i]);
   ^~~~~~~~~~~~~~~~~~

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