cant print value of post

inside div dialog01 i want to echo $ss. but its echo out "no POST". i am not sure how can i echo the value of qty.

index.php

    <?php
    echo"
    <form  method='POST' action='index.php'>

       <input type='text'  name='qty' />

        <button type='submit' id='opener01'  name='b1'>submit</button>

    </form>";

 echo"
<div id='dialog01' title='ccc'> ";
       if(isset($_POST['qty'])){        
               $ss = $_POST['qty'];
                echo $ss;
                }
                else
                {
                echo"NO POST";
               }

    echo"
    </div>";
    ?>

jquery.js

$( "#dialog01" ).dialog({
    autoOpen: false, 
    modal: true,
    buttons: {
        "option1": function() {
            $( this ).dialog( "close" );
         },
        "exit": function() {
            $( this ).dialog( "close" );
        }
    }
});
$( "#opener01" ).click(function() {
      $( "#dialog01" ).dialog( "open" );
      return false;
});