One. The scenario requires that nine out of ten people need to go for +1 instead of +3, or everyone ultimately gets nothing. Assuming that 1/10 of the other people are already accounted for is wiser than assuming that 9/10 are. And at the end of the day the worst case scenario for my choice is that I could have won more, or I lost through circumstances outside of my control. The other option, by contrast, has a worst case scenario of my choice directly contributing to everyone's loss. And even aiming for the smaller pot, I still turn a profit, so I see no reason to be averse to the smaller payout.