/in/foo.cc: In function 'int main()':
/in/foo.cc:10:25: warning: iteration 1000003 invokes undefined behavior [-Waggressive-loop-optimizations]
   10 |                 if (!b[i]) {
      |                      ~~~^
/in/foo.cc:9:27: note: within this loop
    9 |         for (int i = 2; i <= N; i ++) {
      |                         ~~^~~~