/in/foo.cc: In function 'bool is_prime_ll(ll)':
/in/foo.cc:28:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   28 |     for (int i = 0; i < primes.size(); ++i) {
      |                     ~~^~~~~~~~~~~~~~~