jQuery: Counting checked checkboxes

The jQuery Code START
  
  <script type="text/javascript" src="http://code.jquery.com/jquery-latest.js"></script>
    <script type="text/javascript">
      function count() {
        alert("You checked " + $("input:checked").length + " items.");
      }
    </script>
    
    <style type="text/css">
        .code { color: red; }
        .back { background-color: yellow; }
    </style>
  </head>

  <body>
  <h1>jQuery: Counting checked checkboxes</h1>
  
  <form>
    <input type="checkbox">Check 1</input>
    <input type="checkbox">Check 2</input>
    <input type="checkbox">Check 3</input>
    <input type="checkbox">Check 4</input>
    <br />
    <input type="button" value="Count" onclick="count()"></input>
  </form>