Leave menu bar fixed on top when scrolled

gistfile1.js

/* Dynamic top menu positioning
 *
 */

var num = 300; //number of pixels before modifying styles

$(window).bind('scroll', function () {
    if ($(window).scrollTop() > num) {
        $('.navbar').addClass('navbar-fixed-top');
    } else {
        $('.navbar').removeClass('navbar-fixed-top');
    }
});

//http://jsfiddle.net/adamb/F4BmP/