-10 + 1/4(440) = 100It's 110 not 100 as each of the other 3 players are putting in 10 this round.
Each game is independent given equal skill of the players. The EV of each player if you don't play is
-10 + (1/3)330 = 100
The only fair way for you to enter is for you to pay y such that their EV is unchanged,
-10 + 1/4(330 + 110) = 100
-10 + 110 = 100
100 = 100
99999999 = 999999999
tournament gets expensive by my estimations