How to bind the change event of input using lastest rivets

[david]

Consider an example:

<div>
<input type="text" id="number_1"/> x <input type="text" id="number_1"/> = <span id="total"></span>
</div>

When #number_1 textfield is filled in 5 and #number_2 textfield is filled in 2,then #total span will be show 10 automatically.
How to do this by rivets (0.9.6),Please display all the code,thanks very much.