To get the total number of online users, you can bind to a jQuery custom event named iflychat-site-online-users-count as shown below:

jQuery('#drupalchat').bind('iflychat-site-online-users-count', function(event, no) {
  jQuery('#your-div').html('Online users - ' + no); //your code here
});

Your div would then be automatically updated whenever online user count changes.

Note that you should be using a premium plan in order to be able to use this feature.