Can you get pregnant if you have sex on your period?

Nicki • Drown the despresso with espresso ☕
If you have sex on the day your period starts, how likely would it be for you to get pregnant (not using protection)? I know sperm can last like 5 days outside the male body but wouldn't it all be flushed out from your period? (Asking for future reference, I haven't gone and done it already)