var agt=navigator.userAgent.toLowerCase();
var ver;
if (agt.indexOf("msie")>1) ver="ie";
else ver="maz";

var act=0;
var cur_top;
var dest_cur;
var id_timer;
var id_interval;

var destin_top=screen.height/2-260;   //--верхняя граница
var destin_bottom=screen.height;  //--нижняя граница


function  on_scroll() {
/*  if (act==0) {
     act=1;
     cur_top=document.getElementById('act').offsetTop;
     id_timer = setTimeout(set_interval, 200);
  }         */
}
function set_interval() {
   clearTimeout(id_timer);
   dest_cur=Math.round(getBodyScrollTop())+destin_top;
   id_interval = setInterval(act_move, 3);
}

function act_move() {
  if (dest_cur>=cur_top) {
    document.getElementById('act').style.top = document.getElementById('act').offsetTop + 5 + "px";
    if (document.getElementById('act').offsetTop>=dest_cur) {
       document.getElementById('act').style.top=dest_cur+"px";
       act=0;
       clearInterval(id_interval);
    }
  }
  else {
    document.getElementById('act').style.top = document.getElementById('act').offsetTop - 5 + "px";
    if (document.getElementById('act').offsetTop<=dest_cur) {
       document.getElementById('act').style.top=dest_cur+"px";
       act=0;
       clearInterval(id_interval);
    }
  }
}
function getBodyScrollTop() {
   return self.pageYOffset ||
   (document.documentElement && document.documentElement. scrollTop ) ||
   (document.body && document.body. scrollTop );
}