function back_top() 
{ 
        x = document.body.scrollLeft; 
        y = document.body.scrollTop; 
        step = 2; 

        while ((x != 0) || (y != 0)) { 
                scroll (x, y); 
                step += (step * step / 300); 
                x -= step; 
                y -= step; 
                if (x < 0) x = 0; 
                if (y < 0) y = 0; 
        } 
        scroll (0, 0); 
}