sql for first day of month and last day of month

select SYSDATE ,
last_day(sysdate) as LAST_DATE_CURR_MNTH,
ADD_MONTHS(last_day(sysdate),-1) as PREVIOUS_MON_LAST_DATE,
last_day(sysdate)+1 as NEXT_MON_FIRST_DATE,
ADD_MONTHS(last_day(sysdate),+1) as NEXT_MON_LAST_DATE,
ADD_MONTHS(last_day(sysdate),+5) as LAST_DATE_OF_5TH_MON,
ADD_MONTHS(last_day(sysdate),+5) +1 as FIRST_DATE_IN_6TH_MON_AFTR_NOW  
from dual;

"SYSDATE"    "LAST_DATE_CURR_MNTH"    "PREVIOUS_MON_LAST_DATE"    "NEXT_MON_FIRST_DATE"    "NEXT_MON_LAST_DATE"    "LAST_DATE_OF_5TH_MON"   
-----------  ---------------------   ------------------------    ---------------------   --------------------    -----------------------
"FIRST_DATE_IN_6TH_MON_AFTR_NOW"
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01-APR-16        30-APR-16                31-MAR-16                    01-MAY-16                31-MAY-16            30-SEP-16   
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01-OCT-16