$("prodejny").observe('click', function(event){
    var clicked_salesroom = event.findElement('#prodejny li');
    if (clicked_salesroom) {
        id_salesroom = $(clicked_salesroom).id.substr(2);
        $$('.prodejna').each(function(pr){
            pr.removeClassName('visible');
        });
        $("prodejna"+id_salesroom).addClassName('visible');

        $$('#prodejny li').each(function(pr){
            pr.removeClassName('active');
        });
        $("pr"+id_salesroom).addClassName('active');
    }
});