foo.cc: In function 'int main()':
foo.cc:12:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |         for (int j = 0; j < primes.size() && i * primes[j] < n; j++) {
      |                         ~~^~~~~~~~~~~~~~~

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