50, but I'm not so sure the Supreme Court is going to have to rule on this. The circuit courts seem poised to strike down all the remaining bans and the Supreme Court won't need to rule.
Some state Governors and Attorneys-General will file stays that the US Supreme Court will vacate for lack of compelling substance.
I would not be surprised if some states attempt to undo the Supreme Court ruling by legislation to tweak the judgment to offer a worthless permission for SSM, like giving a minimum age of 80, requiring ten years, residency in the state for both applicants... just think of the absurd restrictions.