select sum(position_value) from
(
select power(36,position-1) * case when digit between '0' and '9'
then to_number(digit)
else 10 + ascii(digit) - ascii('A')
end
as position_value
from (
select substr(input_string,length(input_string)+1-level,1) digit,
level position
from (select '01Z' input_string from dual)
connect by level <= length(input_string)
)
)