index.html

<script type="text/JavaScript">
  var dropboxPublicURL = "https://dl.dropboxusercontent.com/u/4121165/xcv58.me/index.txt";

  var xmlHttp = new XMLHttpRequest();
  xmlHttp.open( "GET", dropboxPublicURL, false );
  xmlHttp.send( null );
  var url = xmlHttp.responseText;

  if (/We can't find the page you're looking for/.test(url)) {
    document.documentElement.innerHTML = "<font size=7>"
      + "<a href='" + dropboxPublicURL + "'>"
      + dropboxPublicURL
      + "</a>"
      +" is invalid address!"
      +"</font>";
  } else {
    window.location = url;
  }
</script>