// friend class
#include <iostream.h>

class CSquare;

class CRectangle {
    int width, height;
public:
    int area (void)
    {return (width * height);}
    void convert (CSquare a);
};

class CSquare {
private:
    int side;
public:
    void set_side (int a)
    {side=a;}
    friend class CRectangle;
};

void CRectangle::convert (CSquare a) {
  width = a.side;
  height = a.side;
}
  
int main () {
  CSquare sqr;
  CRectangle rect;
  sqr.set_side(4);
  rect.convert(sqr);
  cout << rect.area();
  return 0;
}