foo.cc: In function 'int main()':
foo.cc:133:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%lld %lld", &n, &m);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~
foo.cc:139:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%lld", &a);
   ~~~~~^~~~~~~~~~~~
foo.cc:145:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%lld", &opt);
   ~~~~~^~~~~~~~~~~~~~
foo.cc:149:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%lld %lld %lld", &l, &r, &x);
    ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:155:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%lld %lld", &l, &r);
    ~~~~~^~~~~~~~~~~~~~~~~~~~~

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