how to get a maximum id from database on from load event

Question

how to get a maximum id from database on from load event and assign the textbox

my storeprocedure is that i am beginer pleae help me

alter PROCEDURE School.GetRegisterationNumber

AS

begin

declare @StudentRegNo int

set @StudentRegNo=(select MAX(StudentRegNo) from School.StudentInformation)

if @StudentRegNo is null

set @StudentRegNo='OXPS-0001'

Return 'OXPS'+'-'+RIGHT('0000'+convert(nvarchar(10),@StudentRegNo),4)

SET @StudentRegNo=SCOPE_IDENTITY()

end

c# code is that  

public int GetRegisterAtionNumber()

{

List<SqlParameter> prm = new List<SqlParameter>();

DataSet ds= rp.GetDS("School.GetRegisterationNumber", prm);

DataTable dt = ds.Tables[0];

return 1;

}

 form load event is that

tbx.tex= GetRegisterAtionNumber().tostring();

 

the error is that

Additional information: Conversion failed when converting the nvarchar value 'OXPS-0333' to data type int.