var isNav = (navigator.appName == "Netscape") ? true : false
var isMac = (navigator.appVersion.indexOf("Mac") != -1) ? true : false
var isFive = (isNav && (navigator.appVersion.charAt(0) >= 5)) ? true : false
var isMacIE = ((navigator.appVersion.indexOf("Mac") != -1)&&(navigator.appVersion.indexOf("MSIE") != -1)) ? true : false
var ie4=document.all
if(ie4){
 if(navigator.appVersion.charAt(22)>=6)var ie6=document.getElementById&&document.all
}
var noprev=true
var str=unescape(window.location.href)
if(str.indexOf("s1.html") != -1)noprev=true
else noprev=false
function GetPrev() {
var str
var newstr=""
str=unescape(window.location.href)

   for (var i = 0; i < str.length; i++) {
      var oneChar=str.charAt(i)
      if(oneChar >= "0" && oneChar <= "9") {
         newstr += oneChar       
      }
   }
    pginst=eval(newstr-1)
window.location.href="s"+pginst+".html"
}
if(!noprev){
document.write('<form><img src="la.gif" onClick="GetPrev()"></form>')
}