My Partner And I Had Sex With A Condom And

My partner and I had sex with a condom and then without it. When he first started, he put on the condom and he decided to take it off. He did not ejaculate inside the condom. He then accidentally put it back in and we took it out when we realized it was in without a condom. There was no ejaculation until the end. What are my chances of being pregnant? Should I take plan b since it will be within 24 hrs?