There are three questions A, B, and C in a mathematics competition. Among the 39 participants, each of them answered at least one question correctly. Among those who answered A correctly, those who only answered A correctly were 5 more than those who also answered other questions correctly; among those who did not answer A correctly, those who answered B correctly were twice as many as those who answered C correctly; The sum of the number of people who only answered C correctly. So how many people can answer A correctly?
一次数学竞赛有A，B，C三题，参赛的39个人中，每人至少答对了一道题．在答对A的人中，只答对A的比还答对其它题目的多5人；在没答对A的人中，答对B的是答对C的2倍；又知道只答对A的等于只答对B的与只答对C的人数之和．那么答对A的最多有多少人．
<gadget id="calculator">6 * 4</gadget>
<output>24</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">4 - 5</gadget>
<output>-1</output>

<gadget id="calculator">24 + (-1)</gadget>
<output>23</output>

<result>23</result>