foo.c: In function 'main':
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d %d",&n1,&n2,&n3);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:8:20: 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:9:20: 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:10:20: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  for(i=0;i<n3;i++) scanf("%d",&a3[i]);
                    ^~~~~~~~~~~~~~~~~~