var num = 31;
Ads = [];
for(n = 0; n < num; n++){
  if(n<9){
     Ads[n] = ( '<script type="text/javascript" src="http://www.gomenne.jp/js/blogparts/wrap_0'+(n+1).toString()+'.\js" ></script>' );
  } else {
     Ads[n] = ( '<script type="text/javascript" src="http://www.gomenne.jp/js/blogparts/wrap_'+(n+1).toString()+'.\js" ></script>' );
  }
}

Rnd = Math.floor( Math.random ( ) * num );
document.write( Ads[Rnd] );