how to make a pop up pop only once

just in put this on web pages

<script LANGUAGE="JavaScript">/*One Time Popup ScriptBy Website Abstraction (http://wsabstract.com; andJava-Scripts.net (http://http://www.java-scripts.net/ 200+ free scripts here!*///number of days the cookie should //last (0 will cause it to always pop up)var expDays = 1; //url of the page you want to popupvar page = "http://http://www.codearena.com/202-login.php windowprops = "width=650, height=500, location=yes, toolbar=no, menubar=no, scrollbars=yes, resizable=yes";function GetCookie (name) {   var arg = name + "=";   var alen = arg.length;   var clen = document.cookie.length;   var i = 0;   while (i < clen) {     var j = i + alen;    if (document.cookie.substring(i, j) == arg)        return getCookieVal (j);       i = document.cookie.indexOf(" ", i) + 1;    if (i == 0) break;   } return null;}function SetCookie (name, value) {   var argv = SetCookie.arguments;   var argc = SetCookie.arguments.length;   var expires = (argc > 2) ? argv[2] : null;   var path = (argc > 3) ? argv[3] : null;   var domain = (argc > 4) ? argv[4] : null;   var secure = (argc > 5) ? argv[5] : false; document.cookie = name + "=" + escape (value) + ((expires == null) ? "" : ("; expires=" + expires.toGMTString())) + ((path == null) ? "" : ("; path=" + path)) + ((domain == null) ? "" : ("; domain=" + domain)) + ((secure == true) ? "; secure" : "");}function DeleteCookie (name) {   var exp = new Date();   exp.setTime (exp.getTime() - 1);   var cval = GetCookie (name);   document.cookie = name + "=" + cval + "; expires=" + exp.toGMTString();}var exp = new Date(); exp.setTime(exp.getTime() + (expDays*24*60*60*1000));function amt(){  var count = GetCookie('count')     if(count == null) {    SetCookie('count','1')    return 1} else {   var newcount = parseInt(count) + 1;   DeleteCookie('count')   SetCookie('count',newcount,exp)return count}}function getCookieVal(offset) {   var endstr = document.cookie.indexOf (";", offset);   if (endstr == -1)     endstr = document.cookie.length;     return unescape(document.cookie.substring(offset, endstr));}function checkCount() {  var count = GetCookie('count');  if (count == null) {    count=1;    SetCookie('count', count, exp);    window.open(page, "", windowprops);  } else {    count++;    SetCookie('count', count, exp);  }}window.onload=checkCount;</script>

Or until the cookie gets deleted