class of 45 people participated in a mathematics competition. As a result, 35 people answered the first question correctly, 27 people answered the second question correctly, 41 people answered the third question correctly, and 38 people answered the fourth question correctly. How many students are there who are correct in all the questions?
某班45人参加一次数学比赛，结果有35人答对了第一题，有27人答对了第二题，有41人答对了第三题，有38人答对了第四题，则这个班四道题都对的同学至少有多少人？
<gadget id="calculator">45 - 35</gadget>
<output>10</output>

<gadget id="calculator">45 - 27</gadget>
<output>18</output>

<gadget id="calculator">45 - 41</gadget>
<output>4</output>

<gadget id="calculator">45 - 38</gadget>
<output>7</output>

<gadget id="calculator">10 + 18 + 4 + 7</gadget>
<output>39</output>

<gadget id="calculator">45 - 39</gadget>
<output>6</output>

<result>6</result>