$(document).ready(function(){
    var index;
    var count;
    var factor;
    var height;
    var roll;
    
    index = 0;
    count = $(".roller .item").length;
    factor = 240;

    roll = function(){
        if ((index + 1) === count) {
            index = 0;
            $(".roller .main").css("margin-top", factor);
        }
        else {
            index += 1;
        }
        height = factor * (index);
        
        $(".roller .main").animate({
            marginTop: (height === 0 ? "0" : "-"+height) + "px"
        }, 1000);
    };
    setInterval(roll, 10000);
});