n = Math.floor(Math.random()*2);
if(n==0)
{str ="<img src='../../../../images/main_img01.jpg' width='655' height='213' border='0'>";}
else if(n==1)
{str ="<img src='../../../../images/main_img02.jpg' width='655' height='213' border='0'>";}

document.write(str);