class Visitor{
	virtual void visit(ConcreteElementA element) = 0;
	virtual void visit(ConcreteElementB element) = 0;
};
class ConcreteVisitor1 :public Visitor{
	void visit(ConcreteElementA element);
	void visit(ConcreteElementB element);
};
class ConcreteVisitor2 :public Visitor{
	void visit(ConcreteElementA element);
	void visit(ConcreteElementB element);
};
class Element{

	virtual void accept(Visitor* visitor) = 0;

};
class ConcreteElementA :public Element{
	void accept(Visitor* visitor);
};
class ConcreteElementB :public Element{
	void accept(Visitor* visitor);
};