Random Number in a loop jquery

I would for every loop an other random number, but it does not want worke... I don't know why.

 $(document).ready(function(){

        setTimeout("execute()",5000);

    })

    function execute(){
        for(i=0;i<5;i++){
            var zWindow = $(window).height();
            var yWindow = $(window).width();
            var z=Math.floor((Math.random() * zWindow) + 1);
            var y=Math.floor((Math.random() * yWindow) + 1);
            $("#egg").css({
                "top": z,
                "left": y
            });
            $("#egg").delay(1000).fadeIn(10).delay(3000).fadeOut(100);
        }

    }