Every digit of an integer greater than 0 is either 7 or 9, but neither all 7 nor all 9, and it is a multiple of 7 and 9. What is the smallest positive integer that satisfies the above conditions?
一个大于0的整数的每一个数字不是7就是9，但不全是7也不全是9，并且它是7和9的倍数，满足上述条件的最小正整数是多少？
<gadget id="calculator">10 ** 0</gadget>
<output>1</output>

<gadget id="calculator">2 * 1</gadget>
<output>2</output>

<gadget id="calculator">10 ** 3</gadget>
<output>1_000</output>

<gadget id="calculator">2 * 1_000</gadget>
<output>2_000</output>

<gadget id="calculator">77_777_777_777 + 2 + 2_000</gadget>
<output>77_777_779_779</output>

<result>77_777_779_779</result>