How to retrieve value from stored procedure using out parameter?

SP

CREATE PROCEDURE GetPasswordOP

    (

   

      @UserName  varchar(50)= '' ,

      @Password varchar(50)= '' ,

      @RtnValue INT OUT

    )

AS

BEGIN

   IF EXISTS (SELECT * FROM tblUserPasswordDetail WHERE UserName = @UserName )

    BEGIN

        SET  @RtnValue = 1;

    END

    ELSE

    BEGIN

        insert into tblUserPasswordDetail(UserName,Password) values(@UserName,@Password)

        set  @RtnValue = SCOPE_IDENTITY()

    END  

END

-------------------------------------------------------------------------------

C# Page

  string Constr = ConfigurationManager.ConnectionStrings["MyDbConn"].ConnectionString;

        SqlConnection con = new SqlConnection(Constr);

        SqlCommand cmd = new SqlCommand("GetPasswordOP", con);

        cmd.CommandType = CommandType.StoredProcedure;

        SqlParameter parm = new SqlParameter("@UserName", SqlDbType.VarChar, 50);

        parm.Value = "abc";

        cmd.Parameters.Add(parm);

        SqlParameter parm2 = new SqlParameter("@Password", SqlDbType.VarChar, 50);

        parm.Value = "abc";

        cmd.Parameters.Add(parm2);

        SqlParameter parm3 = new SqlParameter("@RtnValue", SqlDbType.Int);

        parm3.Direction = ParameterDirection.Output; // This is important!

        cmd.Parameters.Add(parm3);

        con.Open();

        cmd.ExecuteNonQuery();

       

        // Print the output value

        string rtnvalue = cmd.Parameters["@RtnValue"].Value.ToString();

        con.Close();