Select missing number from a column using while loop in SQL Server

hi

this is Estate_info table in database:

and I put lable in page that will bind  Code from table in lable below are codes:

SP:

alter procedure [dbo].[ViewCode]
as
begin
select(select Top 1 code+1
from Estate_info  
order by date desc) as code
end

    private void Viewcode()
    {
        using (SqlConnection conn = General.GetConnection())
        {
            using (SqlCommand _cmd = General.GetCommand("ViewCode", conn))
            {
           
                conn.Open();
                SqlDataReader _dr = _cmd.ExecuteReader();
                while (_dr.Read())
                {
                    Lblcode.Text = _dr["code"].ToString();
                }
            }
        }
    }

now according table it will dispaly:

Lblcode.text==> 15  (Top 1 code+1)...

now here I want if I delete rows from Estate_info Like below:

here I delete row with id=2 so code:11 isn't in table...

now I want at first check table if all number(codes number) be in table after that it does :(select(select Top 1 code+1 from Estate_info   order by date desc) as code

if like above table number wasn't in table it will dispaly that number

i.e:

here I want lblcode display--> 11 (becuse number 11 isn't in table)

how I can do it?

best regards

neda