How to fire an event when i am selecting a date from ajax calendar extendar control?

Question

Hi all...

Here i am using ajax calendar extender control for my calendar in web form.

below is the code

<cc1:CalendarExtender ID="CalendarExtender1" PopupButtonID="StartDate" Format="dd/MM/yyyy" TargetControlID="txtfromdate" runat="server">
</cc1:CalendarExtender>

and I have two text boxes and one calendar control like start date and end date.

When i select start date from first calendar i want to insert a end date automatically......

how can we achieve...

Please help me out....