If your cycles are regular at 28 days from period to period, the likelihood is stronger for the second guy. If not, it could actually be either guy, though the guy who ejaculated inside you is more likely. Since both sex was unprotected, please get checked for STDs. If you do wind up pregnant, write back and I'll give you some info on how to time getting an ultrasound to try to get this estimate more finely tuned.