I want to make calculator for summation.

I have this jquery code:

 <script type="text/javascript">

 $(document).ready(function() {

     $("#calculate").click(function() {

    if ($("#input").val() != '' && $("#input").val() != undefined) {

        $("#result").html("Result is: " + parseInt($("#input").val()) * 30 );

         }

         else
         {
             $("#result").html("Please enter some value");
         }
    }); });

 </script>

<div id="calculator">
    <br />
    <input type="text" style="left:20px;" id="input" />
    <div id="result"></div>
    <input type="button" id="calculate" value="calculate" style="left:20px;" /> 
</div>

I want something like this:

I write number 5, then input + from keyboard and write another value.

Then to click on summation button and to get value.

Can anyone help me with this?

Thank you very much!