/in/foo.cc: In function 'int main()':
/in/foo.cc:14:28: 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=]
  printf("%d", 52 - a.size());
                            ^