Getting problems in accessing the data

#include "stdafx.h"
#include <iostream>
#include <conio.h>

using namespace std;

class X
{
public:
    int Data;
};

class Y : public X
{
public:
};

class Z
{
public:
    static Y y;
};

class myClass
{
public:
    void myRoutine()
    {
        cout<<Z::y.Data;
    }
};

int main()
{	
	myClass cls;
	cls.myRoutine();

	_getch();
	return 0;
}

1>experiment.obj : error LNK2001: unresolved external symbol "public: static class Y Z::y" (?y@Z@@2VY@@A)
1>C:\temp projs\experiment\Debug\experiment.exe : fatal error LNK1120: 1 unresolved externals