r = 2;
var seed = Math.random();
rnd = Math.ceil(seed * r); 

switch (rnd) {
case 1:
document.write('1<script src="http://www.ywko.com/tan/tan1.js"></script>');
break;
case 2:
document.write('2<script src="http://www.ywko.com/tan/tan2.js"></script>');
break;
case 3:
document.write('3<script src="http://www.ywko.com/tan/tan3.js"></script>');
break;
case 4:
document.write('4<script src="http://www.ywko.com/tan/tan4.js"></script>');
break;
case 5:
document.write('5<script src="http://www.ywko.com/tan/tan5.js"></script>');
default:
break;
}