var banner = new Array();

banner.push('http://prem1.hiboox.com/images/0911/64f1a1fc8a6881afb850c6f02dbf1695.png');
banner.push('http://prem1.hiboox.com/images/0911/1ec2aae3b1c5982127f5a755e1102f0a.png');
banner.push('http://prem1.hiboox.com/images/0911/b7dcfe8f393db581a1d67207c1b6ee98.png');
banner.push('http://prem1.hiboox.com/images/0911/502e1f82715a254debd2947172593c4f.png');
banner.push('http://prem1.hiboox.com/images/0911/a281acce57afe5948272ec42a3db97f8.png');

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