<div id="navbar-exapmle" class="navbar" data-spy="affix" data-offset-top="20">
    <ul class="nav navbar-nav affix">
      <li class="active"><a href="#">Link 1</a></li>
      <li><a href="#">Link 2</a></li>
      <li><a href="#">Link 3</a></li>
    </ul>
  </div>