var banner = new Array();

banner[0]='https://i.servimg.com/u/f46/17/16/10/26/banner18.jpg';
banner[1]='https://i.servimg.com/u/f46/17/16/10/26/banner19.jpg';
banner[2]='https://i.servimg.com/u/f46/17/16/10/26/banner20.jpg';

document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];
setInterval("document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];",30000);