var timerID;

function fnSlider() {

  var speed = 2;
  var sliderObj = document.getElementById('slider');
  var slider2Obj = document.getElementById('slider2');
  var contentHeight = sliderObj.offsetHeight;
  var contentHeight2 = slider2Obj.offsetHeight;


  if (parseInt(sliderObj.style.top) == 0 && parseInt(slider2Obj.style.top) == 0) {
    slider2Obj.style.top = "-" + contentHeight2 + "px";
  }

  if (parseInt(sliderObj.style.top) >= 0 && parseInt(sliderObj.style.top) <= 2) {
    slider2Obj.style.top = "-" + contentHeight2 + "px";
  }

  if (parseInt(slider2Obj.style.top) >= 0 && parseInt(slider2Obj.style.top) <= 2) {
    sliderObj.style.top = "-" + contentHeight + "px";
  }

  slider2Obj.style.top = parseInt(slider2Obj.style.top) + speed + "px";
  sliderObj.style.top = parseInt(sliderObj.style.top) + speed + "px";


  timerID = setTimeout('fnSlider()', 50);

}

window.onload = fnSlider;