<!-- jQuery (necessary for Bootstrap's JavaScript plugins) -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<!-- Include all compiled plugins (below), or include individual files as needed -->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>

<script src="jquery-1.11.3.min.js"></script>

<script>

    $(document).ready(function () {
        var NavY = $('.nav').offset().top;

        var stickyNav = function () {
            var ScrollY = $(window).scrollTop();

            if (ScrollY > NavY) {
                $('.navbar').addClass('navbar-fixed-top');
            } else {
                $('.navbar').removeClass('navbar-fixed-top');
            }
        };

        stickyNav();

        $(window).scroll(function () {
            stickyNav();
        });
    });

</script>