javascript input and checking math function

<input name="searchTxt" type="text" maxlength="512" id="searchTxt" class="searchField"/>
<p id="text"></p>
<script>
var input = document.getElementById("searchTxt");
document.getElementById('text').innerHTML = input.value;</script>

I'm typing in the input and the text should appear below,but it doesn't and I dont know why, does anybody know what the problem might be?