function countdown (seconds_left) {
  countdown_minutes=Math.floor (seconds_left / 60).toString();
  countdown_seconds=Math.floor (seconds_left % 60).toString();

  if (countdown_minutes.length < 2)
    countdown_minutes = "0" + countdown_minutes;

  if (countdown_seconds.length < 2)
    countdown_seconds = "0" + countdown_seconds;

  if (seconds_left <= 0) {
   document.getElementById('counter').style.display='none';
   document.getElementById('expired').style.display='block';

   return
  }
  else {
   document.getElementById('countdown_min').innerHTML=countdown_minutes;
   document.getElementById('countdown_sec').innerHTML=countdown_seconds;

   next = seconds_left - 1;
   setTimeout ("countdown (next)", 1000)
  }
}

countdown (2400);