Dice game II

You can roll a $6$-side dice up to $3$ times. After the first or the second roll, if you get a number x, you can decide either to get $x$ dollars or to choose to continue rolling. But once you decide to continue, you forgo the number you just rolled. If you get to the third roll, you'll just get $x$ dollars if the third number is $x$ and the game stops. What is the game worth and what is your strategy?