Find month first day and last day in sap abap

INITIALIZATION.
w_tmp_date = sy-datum.

CONCATENATE w_tmp_date(6) '01' INTO w_first_date.

CALL FUNCTION 'HR_HCP_GET_LAST_DAY_OF_MONTH'
EXPORTING
im_date = w_tmp_date
IMPORTING
ex_last_day_of_month = w_last_date.


s_date-low = w_first_date.
s_date-high = w_last_date.
s_date-sign = 'I'.
s_date-option = 'EQ'.

APPEND s_date.