I'm guessing you mean sperm and vagina and pregnant. As stated above it only takes one sperm to meet one egg and if it implants you will be pregnant. No one can tell you how many times this will take. God only knows why some people get pregnant on the first try and others never succeed.
One sperm out of the millions that are ejaculated just one time, or even expressed in pre-ejaculation, is all it takes to get pregnant.
I hope you're asking this to try to avoid pregnancy.
All it takes is one time. If you don't want a baby use protection!!
One drop can do the trick if ur trying to have a baby u should know that...