Can I use Windows Server 2003 product key on Windows Server 2003 R2?

I need to do a fresh installation on the server running W2003 Std Edition (32-bit) but don’t have the original CD. However, I do have W2003 Std R2 Edition (32-bit) CD. My query is, can the same Product key be accepted to work during the installation of W2003 Std R2 Edition?