function xx (){
var left_h = document.getElementById("leftblock").offsetHeight;
var main_h = document.getElementById("mainblock").offsetHeight;
var footer_h = document.getElementById("footer").offsetHeight;
var th;
var foot;

if (navigator.appName == "Microsoft Internet Explorer") {

var win_h = document.body.offsetHeight;

if (main_h > left_h) {
if (main_h + footer_h > win_h) { th = main_h; }
if (main_h  + footer_h < win_h) { th = win_h - footer_h - 4; }
}

if (left_h > main_h) {
if (left_h + footer_h > win_h) { th = left_h; }
if (left_h + footer_h < win_h) { th = win_h - footer_h - 4; }
}
}




else {

    var win_h = window.innerHeight;

    if (main_h > left_h) {
        if (main_h + footer_h > win_h) { th = main_h; }
        if (main_h  + footer_h < win_h) { th = win_h - footer_h - 2; }
    }

    if (left_h > main_h) {
        if ((left_h + footer_h) > win_h) { th = left_h; }
        if ((left_h + footer_h) < win_h) { th = win_h - footer_h - 2; }
    }
}


    //alert(navigator.appName);
   
    foot = th + "px";
    //alert(foot);
    return foot;

}