Procedure Retruning Value

Alter Procedure sp_DuplicateClientCode
(
@ClientCode nvarchar(max))
as
begin
Declare @Duplicate int
if exists(select * from ItSchool_ClientUserPass_Mst where ClientCode=@ClientCode)
 set @Duplicate=1
 else
 set @Duplicate=0
 return @Duplicate
end


SqlConnection con = new SqlConnection(constr);
        SqlCommand cmdD = new SqlCommand("sp_DuplicateClientCode", con);
        cmdD.CommandType = CommandType.StoredProcedure;
        cmdD.Parameters.Add("@ClientCode", SqlDbType.VarChar).Value = txtccode.Text;
        var returnParameter = cmdD.Parameters.Add("@Duplicate", SqlDbType.Int);
        returnParameter.Direction = ParameterDirection.ReturnValue;
        con.Open();
        cmdD.ExecuteNonQuery();
        var result = returnParameter.Value;      
        con.Close();