function bindShopForm(selector, url){
    $(selector).click(function(){
        var tag_a = $(this);
        var field = $(tag_a.attr('rel'));
        var value = parseInt(field.val());
        if (isNaN(value) || value < 1){
            alert('Wrong quantity!');
            field.focus();
            return false;
        }
        window.location.href = tag_a.attr('href')+'?qty='+value;
        return false;
    });
}