foo.cc: In function 'int main()':
foo.cc:13:12: warning: iteration 101 invokes undefined behavior [-Waggressive-loop-optimizations]
      if(a[j]>0)t=t+1;
         ~~~^
foo.cc:12:18: note: within this loop
     for(int j=0;j<=2001;j++){
                 ~^~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。