url = new Array();

url[0] = "recruit/index-01.html";
url[1] = "recruit/index-02.html";
url[2] = "recruit/index-03.html";
url[3] = "recruit/index-04.html";

function jump() {
   p = Math.round(Math.random() * (url.length - 1));
   parent.top.document.location = url[p];
}