Scenario:

3 people in my office are playing a golf game for money. The rules are a cup is placed at one end of the room and the goal is to putt a golf ball into the cup. Each person puts £10 into the pot and gets 1 shot. If no one scores or everyone scores, they all play another round, again putting £10 each into the pot until only 1 person scores who takes the pot. If 2 people score and one misses then the misser is out and the game continues with the remaining 2 people.

I enter the room, the pot contains £300 with all 3 players who began the game still active. I want to join the game.

Assuming equal golf skill and a fair game, what amount should I add to the pot be fair to all parties for me to join the game at this point?