How can I get return value from Store Procedure within SqlDataSource in ASP.net

Hi I am new to this.
I don't get any value back when I execute my code.but when I execute the SP I can get the value 47.
Please help.
Thanks in advance.
The following is detail
        <asp:SqlDataSource ID="SqlDataSource2" runat="server"
            ConnectionString="<%$ ConnectionStrings:EDIConnectionString %>"
            OnSelecting="SqlDataSource2_Selecting"
            SelectCommand="FailedCreateSO" SelectCommandType="StoredProcedure" >
            <SelectParameters>
                <asp:Parameter DefaultValue="0" Direction="InputOutput" Name="NOOfFAILEDTRX"
                    Type="Int32" />
            </SelectParameters>
        </asp:SqlDataSource>

SP

CREATE PROCEDURE FailedCreateSO @NOOfFAILEDTRX INT OUTPUT
as

SELECT @NOOfFAILEDTRX = COUNT(*)  FROM EDITRX850_IN WHERE (Status = 'E') AND (TransferToOracleDate > GETDATE() - 200)
GO

Code
        protected void SqlDataSource2_Selecting(object sender, SqlDataSourceSelectingEventArgs e)
        {

            int test;
            test = (int)e.Command.Parameters["@NOOfFAILEDTRX"].Value
           
        }