first day of the year

hi
in oracle form , how i can return first day of the year for a given date
field name is : :BASIC_BLOCK.c_per
i found this function
SELECT TRUNC(to_date('17-DEC-2001'),'YEAR') "First Day" FROM Dual;
but it doesnt work when i replaced it like this
declare
begd date;
begin
SELECT to_date(:BASIC_BLOCK.c_per ,'Yyyy-mm-dd') into begd  FROM Dual;