ResponsiveSlides – Current slide number

Question

I’m using ResponsiveSlides.js to display a slideshow on my website: http://moargh.de/daten/responsive-slides/demo/demo.php

Can anybody help how to display the current slide number?

jQuery

$(function () {

var total = $('ul#slider4 > li').length; 

  $("#slider4").responsiveSlides({
    auto: false,
    pager: false,
    nav: true,
    speed: 500,
    namespace: "callbacks",
  });

  $('.total-slides').html(total);

});

HTML

  <ul class="rslides" id="slider4">
    <li>
      <img src="images/1.jpg" alt="">
      <p class="caption">This is a caption</p>
      Slide X of <span class="total-slides"></span>
    </li>
    <li>
      <img src="images/2.jpg" alt="">
      <p class="caption">This is another caption</p>
      Slide X of <span class="total-slides"></span>
    </li>
  </ul>

Thanks!