Oracle - SQL - Select - Select Count

SELECT COUNT(*) FROM 
(
SELECT a.*, b.CMPY_N, b.CUST_ACNT_N FROM [BeaconPhase2_DEV].[BCN].[AGENTS_LOG_MSG] a LEFT JOIN 
[BeaconPhase2_DEV].[BCN].[CUST_STATIC] b ON a.CUST_K = b.CUST_K
) AS subquery;