a, b, c are all prime numbers, and a+b=33, b+c=44, c+d=66, then cd=how many.
a，b，c都是质数，并且a+b=33，b+c=44，c+d=66，那么cd=多少．
<gadget id="calculator">33 - 2</gadget>
<output>31</output>

<gadget id="calculator">44 - 31</gadget>
<output>13</output>

<gadget id="calculator">66 - 13</gadget>
<output>53</output>

<gadget id="calculator">53 * 13</gadget>
<output>689</output>

<result>689</result>