Period sex

Okay I know this may be gross to some people but anyway me and my boyfriend had sex today. Today is the first day of my period so I wondered what are the chances of getting pregnant if I have unprotected sex on my period and he pulls out before cums? I know it's not the smartest thing to do but I just need to know tha chances my periods are usually 7 days long and I usually ovulate a week or two before my period. Thanks