var i=0;
var scroll_break=1;

function scroll_up(){
    if (i>=40)
        i=i-40;
    else if (i<40 && i>=0)
        i=0;
    document.getElementById('main').scrollTop=i;
    if (scroll_break)
        setTimeout('scroll_up();', 100);
    else
        scroll_break=1;
}
function scroll_down(){
    var scroll=document.getElementById('main').scrollTop;
    if ((i-5)<=scroll)
        i=i+40;
    else if ((i-5)>scroll)
        i=scroll;
    document.getElementById('main').scrollTop=i;
    if (scroll_break)
        setTimeout('scroll_down();', 100);
    else
        scroll_break=1;
}
function scroll_breaker(){
    scroll_break=0;
}