foo.cc: In function 'void Std::main()':
foo.cc:68:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   68 |         scanf("%lld%lld",&n,&m);
      |         ~~~~~^~~~~~~~~~~~~~~~~~
foo.cc: In function 'void Std::get_prime()':
foo.cc:13:23: warning: iteration 49999 invokes undefined behavior [-Waggressive-loop-optimizations]
   13 |             if(!mark[i])
      |                 ~~~~~~^
foo.cc:11:21: note: within this loop
   11 |         for(ll i=2;i<=50001;i++)
      |                    ~^~~~~~~

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