#include <iostream>
using namespace std;
class Y;
class Z;
class X {
int x;
public:
X(int n = 0) { x = n; }
friend Y;
};
class Y {
int y;
friend Z;
};
class Z {
public:
void f(X u) { cout << u.x; }
};
int main()
{
X a;
Z b;
b.f(a);
}