That is precisely when you get pregnant! Ok- I'm gonna lay this out for you! Pay attention. Your body ovulates (pops out an egg) 10-14 days after the FIRST day of your last period. Sperm lives for 3-5 days. So let's say you have a regular 5 day cycle, and on day 6 you go out and have sex. His swimmers live inside you for 3-5 days, you ovulate on day 10 and POOF... the magic of conception occurs! I practiced the rhythm method for 5 years, so I know exactly how it works, but there is seriously like 2.5 weeks you have to avoid sex. Please go on the pill to prevent pregnancy and use a condom to protect yourself from STD's
While it is less likely that you would get pregnant - anytime that you have unprotected sex, there is a chance you could get pregnant. So there is no reason (unless one is looking to get pregnant) not to practice safe sex.