function back_top()
{
        x = document.body.scrollLeft;
        y = document.body.scrollTop;
        step = 5;

        while ((x != 0) || (y != 0)) {
                scroll (x, y);
                step += (step * step / 100);
                x -= step;
                y -= step;
                if (x < 0) x = 0;
                if (y < 0) y = 0;
        } 
        scroll (0,0);
}