Two players P1 and P2 agree to play the following game. Each puts up a stake of 1 unit. They will play seven rounds, where each round involves flipping a fair coin. If the coin comes up H, P1 wins the round, otherwise P2 wins. The first player to win four rounds gets both stakes. After four rounds, P1 has won three rounds and P2 has won one round, but they have to stop. What is the fairest way to divide the stakes?