need help in database connectivity in c#

Question

im beginner to c# ,asp.net and mysql

i write a program to access some data from mysql server.thats works fine

but i want to select a max value of a field. how can i access that value from data reader . i tried many ways . but...

code is given below

MySqlConnection con = new MySqlConnection();

            con.ConnectionString = "Data Source=localhost;Database= mydatabase;User ID=root;Password=vox";

            con.Open();

            string str;

            str = string.Format("select max(user_id)  from usertable");

            MySqlCommand cmd = new MySqlCommand(str, con);

            MySqlDataReader dr;

            dr = cmd.ExecuteReader();

how can i get that max value of user_id from data reader.

thanks in advance