title: Task.Continuewith equivalent in RX
body: <p>I have a scenario to start a subscription once another subscription is completed. Both are sharing the same connected stream.</p>
  
  <pre><code>IConnectableObservable&lt;List&lt;int&gt;&gt; stream = GetMyHotStream();
  var firstSubscription = stream.Subscribe(s=&gt;{});
  var secondSubscription = stream.Subscribe(s=&gt; {});
  stream.Connect();
  </code></pre>
  
  <p>Now I would like to wait the <code>secondSubscription</code> until the <code>firstSubscription</code> is finished.</p>
  
  <p>I omitted other details for brevity.</p>
  
  <p>Any answer will be very helpful.. Thanks</p>