foo.cc: In function 'int main()':
foo.cc:17:33: warning: iteration 999 invokes undefined behavior [-Waggressive-loop-optimizations]
   17 |  for(int i=1;i<=1000;i++) if(a[i]==1) ans++;
      |                              ~~~^
foo.cc:17:15: note: within this loop
   17 |  for(int i=1;i<=1000;i++) if(a[i]==1) ans++;
      |              ~^~~~~~

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