Please help- serious answers only?!

Please help- serious answers only?

I had my period for four days. Four days after the last day of my period my boyfriend's condom fell off inside of me during sex. I know there are so many rules to "x" amount of days in you cycle blah blah that you are fertile, but I was wondering for the people who really know the explanation well, is there a chance I could possibly end up pregnant?

I know that "it only takes one time", and that"if you have sex there is always a chance no matter what".... but please for the people who know the facts... I would appreciate the help.

I think that on the eighth day there is a chance. Not a big one, but still... Maybe you could try getting the morning after pill, just to be on the safe side.