#include <iostream>
using namespace std;
class B {
int x;
public:
B(int i = 10) { x = i; }
int get_x() { return x; }
};
class D : public B {
public:
D(int i)
: B(i)
{
}
D operator+(const D& a) { return x + a.x; }
};
int main()
{
D ob1(7), ob2(-12);
cout << (ob1 + ob2).get_x();
return 0;
}