using 2 CollapsiblePanelExtenders for 2 panels,want collapse one at a time

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I am using 2 panels and 2 CollapsiblePanelExtenders. I would like to make these collapsible one at a time.
I am using visual studio 2005.
My javascript code gives error and doesn't work
Code is

        function pageLoad(sender, args) {           
            for (num = 1; num < 3; num++) {
                $find("CollapsiblePanelExtender" + num).add_expandComplete(coll_ExpandedComplete);               
            }
        }
 
        function coll_ExpandedComplete(sender, arg) {           
            for (num = 1; num < 3; num++) {
var CollapsiblePanel = $find("CollapsiblePanelExtender" + num);
if (sender._expandControlID != CollapsiblePanel._expandControlID)
                    CollapsiblePanel.collapsePanel(CollapsiblePanel._expandControlID);
            }          
        }               

Please give me the solution.