-std::shared_ptr<Step> find_path(const std::string& start, const std::string& goal);
-std::shared_ptr<Step> find_path(const Board& start, const Board& goal);
+std::shared_ptr<Step> find_path(const std::string& start, const std::string& goal, unsigned max_frontier);
+std::shared_ptr<Step> find_path(const Board& start, const Board& goal, unsigned max_frontier);