#include <iostream> 
 
class A 
{ 
public: 
 virtual ~A() = 0; 
}; 
 
A::~A() 
{ 
} 
 
class B: public A 
{ 
}; 
 
int main() 
{ 
 A* a = new B; 
 delete a; 
 
 return 0; 
}