#include <iostream>
using namespace std;

class A {
public:
    A() { f("A()"); }
    ~A() { f("~A()"); }
protected:
    virtual void f(const char* str) = 0;
};

class B : public A {
public:
    B() { f("B()"); }
    ~B() { f("~B()"); }
protected:
    void f(const char* str) { cout<< str << endl; }
};

int main() {
    B b;
    return 0;
}