What are the chances of getting pregnant on the first try?

Madalys
Has anyone gotten pregnant on only having sex once? 
​I've been with my partner for 4 years. Unprotected sex, never got pregnant 
I went to a party and I got really  messed up. Point is someone took advantage of me while I was passed out. When I woke up I told him to stop and he pulled out and ejaulated on the couch (and all over me).  That same week I was having sex unprotected with my boyfriend. 
​I would like your opinion on who you think the dad is?