Preciso de ajuda com o bootstrap nav. Quero que seja alternado através de um ícone de hambúrguer no celular.

Aqui está no codepen:http://codepen.io/sadman/pen/hfGwv (link inválido)

.navbar,
.navbar-inverse {
  border-radius: 0;
  border: none;
  margin-bottom: 0;
  min-height: 80px;
}

.nav li {
  display: inline;
  color: white;
}

.navbar-inverse .navbar-nav>li>a {
  color: #ffffff;
  font-family: Lato;
  font-size: 1.7em;
  font-weight: 300;
  padding: 30px 25px 33px 25px;
}

.navbar-inverse .navbar-nav li a:hover {
  background-color: #444444;
  transition: 0.7s all linear;
  height: 100%;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.min.css">

<nav class="navbar navbar-inverse navbar-static-top" role="navigation">
  <div class="container">
    <ul class="nav navbar-nav">
      <li><a href="index.php">Home</a></li>
      <li><a href="about.php">About</a></li>
      <li><a href="#portfolio">Portfolio</a></li>
      <li><a href="#">Blog</a></li>
      <li><a href="contact.php">Contact</a></li>
    </ul>
  </div>
</nav>