SQL & PL/SQL

Hi everybody, starting from a number X, I need to retrieve the number of days.
For example:

X = 10 -> number of days = 0
X = 12 -> number of days = 0,5
X = 24 -> number of days = 1
X = 25 -> number of days = 1
X = 34 -> number of days = 1
X = 36 -> number of days = 1,5
X = 37 -> number of days = 2
X = 72 -> number of days = 3
X = 70 -> number of days = 3

I tried with ROUND(X) but it didn't work as I wanted, because with 36 it retrieve 2 (instead of 1,5).
Practically, half a day (12 hours) have to be considered ALWAYS as 0,5 and NOT rounded.

Any idea ?
Thanks in advance

Alex