foo.cc: In function 'int main()':
foo.cc:6:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d",&n1,&n2,&n3);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~~
foo.cc:10:28: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for(int i=0;i<n1;i++)scanf("%d",&a[i]);
                       ~~~~~^~~~~~~~~~~~
foo.cc:11:28: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for(int i=0;i<n2;i++)scanf("%d",&b[i]);
                       ~~~~~^~~~~~~~~~~~
foo.cc:12:28: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for(int i=0;i<n3;i++)scanf("%d",&c[i]);
                       ~~~~~^~~~~~~~~~~~