title: why can't I install Google Cloud Messaging for Android Library
body: <p>I'm following the instruction about using gcm here <a href="http://developer.android.com/guide/google/gcm/gs.html" rel="noreferrer">http://developer.android.com/guide/google/gcm/gs.html</a>, and I'm stuck at the following step: </p>
  
  <p><strong>Install the Helper Libraries</strong>
  To perform the steps described in the following sections, you must first install the helper libraries (reference: client and server). From the SDK Manager, <strong>install Extras > Google Cloud Messaging for Android Library</strong>. This creates a gcm directory under YOUR_SDK_ROOT/extras/google/ containing these subdirectories: gcm-client, gcm-demo-appengine, gcm-demo-client, gcm-demo-server, and gcm-server.</p>
  
  <p>In my SDK manager, I can't find the option: Google Cloud Messaging for Android Library, as I captured in this screenshot <img src="https://i.stack.imgur.com/ITHPH.png" alt="enter image description here">, what I should do to resolve this? Thanks</p>