datapicker doesn't work! what's the problem?

datapicker doesn't work! what's the problem?

I copy the code from the web,why it can not show the calendar?


<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>jQuery UI Draggable - Default functionality</title>
  <link rel="stylesheet" href="jquery-ui-1.10.4.custom/css/ui-lightness/jquery-ui-1.10.4.custom.css">
  <script src="jquery-ui-1.10.4.custom/js/jquery-1.10.2.js"></script>
  <script src="jquery-ui-1.10.4.custom/js/jquery-ui-1.10.4.custom.js"></script>
  <link rel="stylesheet" href="jquery-ui-1.10.4.custom/development-bundle/demos/demos.css">
 <script>
  $(function() {
    $( "#datepicker" ).datepicker();
  });
  </script>
</head>
<body>
 
<p>Date: <input type="text" id="datepicker"></p>
 
 
</body>
</html>