Among all the parts under the type "promo brushed steel", how many of them have a total available quantity from all suppliers of under 5000?
type "promo brushed steel" refers to p_type = 'PROMO BRUSHED STEEL'; a total available quantity of under 5000 refers to sum(ps_availqty) < 5000
SELECT SUM(num) FROM ( SELECT COUNT(T3.s_name) AS num FROM part AS T1 INNER JOIN partsupp AS T2 ON T1.p_partkey = T2.ps_partkey INNER JOIN supplier AS T3 ON T2.ps_suppkey = T3.s_suppkey WHERE T1.p_type = 'PROMO BRUSHED STEEL' GROUP BY T2.ps_partkey HAVING SUM(T2.ps_availqty) < 5000 ) T