foo.cc: In function 'int main()':
foo.cc:35:23: warning: variable 'b' set but not used [-Wunused-but-set-variable]
   35 |                 int a,b; a=read(),b=read();
      |                       ^
foo.cc:41:25: warning: iteration 100009 invokes undefined behavior [-Waggressive-loop-optimizations]
   41 |                 if(cnt[i]==2) res++;
      |                    ~~~~~^
foo.cc:40:22: note: within this loop
   40 |         for(int i=1;i<=N;i++)
      |                     ~^~~

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