5-4-2

#include <iostream>

using namespace std;
class A
{
public:
    void display(){cout<<x<<endl;}
    int getX() {return x;}
    friend class B;
private:
    int x;
};
class B
{
public:
    void set(int i);
    void display()
    {
        a.display();
    };
private:
    A a;
};

void B::set(int i)
{
    a.x=i;
}
int main()
{
    cout << "Hello world!" << endl;
    B a;
    a.set(9699);
    a.display();
    return 0;
}