/in/foo.cc: In function 'int ck(std::string, std::string)':
/in/foo.cc:171:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  171 |         for (int i = 0; i < a.size(); i++) {
      |                         ~~^~~~~~~~~~