How to get Oracle current session id ?

How to get Oracle current session id ?

Oracle my session 


ALTER SESSION SET nls_date_format='DD-MON-YYYY HH24:MI:SS';
set linesize 300
col PROGRAM for a50
col MACHINE for a30
SELECT sid, serial#,con_id,MACHINE ,PROGRAM FROM SYS.V_$SESSION WHERE SID = (SELECT DISTINCT SID FROM SYS.V_$MYSTAT);

-- To kill 
set page 0
select 'alter system kill session '''||sid||','||serial#||''' IMMEDIATE;' FROM SYS.V_$SESSION WHERE SID = (SELECT DISTINCT SID FROM SYS.V_$MYSTAT);
set page 80