Dice Sum Game

A game is played with two fair six-sided dice. You roll both dice once. If the sum of the two dice is 7, you receive a payout of €21 (the entry fee is not refunded); otherwise you receive nothing. You must pay an entry fee to play each time you roll.

If you are risk-neutral, what is the maximum entry fee (in euros) you would be willing to pay per roll, i.e. the fair price of the game? Give the answer as a decimal number.