Probably an odd question...

So, my SO and I don't exactly have the most forgiving of schedules (I'm at school and work, and he works long nights), so Wednesday will be the next foreseeable day that I have him all to myself, which will also be the fifth day of my period.
If we have unprotected sex, what's the likelihood of my getting pregnant? (Not on any BC)
(Included for those that would like to see cycle length and estimated fertility window.)