Highest value reading Data Base Coloumn

Hello,

 

 I am using bellow command to check max value of column .It works upto 10 after that it  sends always 10 though my data base already increased upto 13 rows.

 

I also checked  SELECT ISNULL (MAX(ID)+1,0)

                            SELECT ISNULL (MAX(ID),0)

 

Please suggest me what to do. 

SqlCommand cmd = new SqlCommand("SELECT ISNULL (MAX(ID)+1,1) AS Result FROM CustomerDetail", con);