There are 40 people in Class 4, 15 of them can play international chess, 23 can play Chinese chess, and 10 can play neither. How many people can play both kinds of chess?
四1班有40人，其中15人会下国际象棋，23人会下中国象棋，两种象棋都不会下的有10人．两种象棋都会下的有多少人？
<gadget id="calculator">10 - 40</gadget>
<output>-30</output>

<gadget id="calculator">15 + 23 + (-30)</gadget>
<output>8</output>

<result>8</result>