/in/foo.cc: In function 'int main()':
/in/foo.cc:14:14: warning: format '%d' expects argument of type 'int', but argument 2 has type 'std::set<std::__cxx11::basic_string<char> >::size_type' {aka 'long unsigned int'} [-Wformat=]
   14 |     printf("%d", 52 - a.size());
      |             ~^   ~~~~~~~~~~~~~
      |              |      |
      |              int    std::set<std::__cxx11::basic_string<char> >::size_type {aka long unsigned int}
      |             %ld