function CountDown()
{
   var COUNTER_ID = "COUNT_DOWN";

   var counterElement = document.getElementById(COUNTER_ID);

   if( !counterElement )
   {
      throw new Error('"COUNT_DOWN" element id not found');
   }

   var ticks = parseInt(counterElement.innerHTML);

   var timer = setInterval(
   function()
   {
      if( ticks )
      {
         counterElement.innerHTML = --ticks;
      }
   }
   , 1000);
}