#include <iostream>
using namespace std;
class Animal {
public:
    virtual void speak() {
        cout << "Animal speak";
    }
};
class Dog : public Animal {
public:
    void speak() {
        cout << "Wang Wang";
    }
};
int main() {
    Animal* p = new Dog();
    p->speak();
    delete p;
    return 0;
}