var banner = new Array();

banner[0]='https://i.servimg.com/u/f49/15/19/37/88/ba1_bm10.jpg';
banner[1]='https://i.servimg.com/u/f49/15/19/37/88/ba2_bm11.jpg';
banner[2]='https://i.servimg.com/u/f49/15/19/37/88/ba3_bm10.jpg';
banner[3]='https://i.servimg.com/u/f49/15/19/37/88/ba5_bm10.jpg';
banner[4]='https://i.servimg.com/u/f49/15/19/37/88/ba6_bm10.jpg';
banner[5]='https://i.servimg.com/u/f49/15/19/37/88/ba4_bm10.jpg';
document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];