There are three numbers A, B, and C. The greatest common factor of A and B is 18, and the greatest common factor of B and C is 12. What is the greatest common factor of the three numbers A, B, and C?
A、B、C三个数，A、B的最大公因数是18，B、C的最大公因数是12，A、B、C三个数最大公因数是多少．
<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<result>6</result>