using namespace std;
#include<iostream>
class A
{
public:
A()
{
std::cout << "A\n";
}
};
class B: public A
{
public:
B()
{
std::cout << "B is derived class\n";
}
};
int main()
{
A * a=new A(); //valid
B * b=new B(); //valid
A * aa=new B(); //valid
B * bb=new A(); //invalid
return 0;
}