Html outputting someones username they enter?

[Jason Jack]

so i have this
<?php
if(isset($_POST['submit'])) {
$username = $_POST['username'];
echo "your username is $username";
}

?>
<form id="form1" name="form1" method="post" action="">
<p>username:
<input type="text" name="username" id="username" />
</p>
<p>
<input type="submit" name="submit" id="submit" value="Submit" />
</p>
</form>

so how would i in the html body say something like,
Hello Jack (jack being the username the user entered)