<!DOCTYPE html>
<html>
<head>
  <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  <script type="text/javascript">
    function show() {
      var results = /\?topic=(.+)$/.exec(window.document.location);
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      var node = document.getElementById("topic");

      node.textContent = topic;
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</head>

<body onload="show()">
  <div id="topic"></div>
</body>
</html>