maximum of sums

Howdy all!

Let's say we have a product orders table like this:

SQL> select * from orders;
ORDER_NO   PROD_NO  QUANTITY
--------- --------- ---------       1         2         3       2         2         3       3         3         3
4        1         4       5         3         8       6         2         7       7         1         6       8
1         3       9         3         3      10         2         4
 

10 rows selected.

SQL>

I want to select the prod_no and sum (quantity) for the product with the max sum
(quantity).

I have this so far:
SQL> select 2     max (sumamt) as maximum 3  from 4     (select 5        sum (orders.quantity) as sumamt 6      from 7
     orders 8      group by 9        orders.prod_no);
 
 MAXIMUM
---------      17

SQL>

But how can I get the matching prod_id?

Any help would be much appreciated!

Rob