foo.cc: In function 'void input()':
foo.cc:13:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d",&n1,&n2);
  ~~~~~^~~~~~~~~~~~~~~~
foo.cc:14:44: 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].x),a[i].id=i;
                         ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~
foo.cc:15:44: 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].x),b[i].id=i;
                         ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~

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