/in/foo.cc: In function 'int main()':
/in/foo.cc:17:9: warning: iteration 399999 invokes undefined behavior [-Waggressive-loop-optimizations]
   17 |   dp[i] = dp[i - 1] + isAClassNumber(i);
      |   ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/in/foo.cc:16:20: note: within this loop
   16 |  for (int i = 1; i <= 400000; ++i) {
      |                  ~~^~~~~~~~~