What will be the output of the program given below?

#include<iostream.h> 
class AptitudeBase
{
    int x;
    public:
    AptitudeBase(int xx = 0)
    {
        x = xx; 
    }
    void Display()
    {
        cout<< x ;
    }
};
class AptitudeDerived : public AptitudeBase
{
    int y; 
    public:
    AptitudeDerived(int yy = 0)
    {
        y = yy;
    }
    void Display()
    {
        cout<< y ;
    }
};
int main()
{
    AptitudeBase objBase(10); 
    AptitudeBase &objRef = objBase;

    AptitudeDerived objDev(20); 
    objRef = objDev;

    objDev.Display(); 
    return 0; 
}