foo.c: In function 'main':
foo.c:30:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d",&n1,&n2,&n3);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:31:20: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  for(i=0;i<n1;i++) scanf("%d",&a1[i]);
                    ^~~~~~~~~~~~~~~~~~
foo.c:32:20: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  for(i=0;i<n2;i++) scanf("%d",&a2[i]);
                    ^~~~~~~~~~~~~~~~~~
foo.c:33:20: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  for(i=0;i<n3;i++) scanf("%d",&a3[i]);
                    ^~~~~~~~~~~~~~~~~~