There is a two-digit number \overline{ab} and its inverse number \overline{ba} are both prime numbers. For example, 13 and 31 are both prime numbers. What is the possible maximum value of the sum of \overline{ab} and \overline{ba} that satisfies the above conditions?
有一个二位数\overline{ab}与它的逆序数\overline{ba}都是质数．例如，13与31都是质数，请问满足上述条件的\overline{ab}与\overline{ba}之和的可能最大值是多少．
<gadget id="calculator">79 + 97</gadget>
<output>176</output>

<result>176</result>