Hongguang Primary School has set up two interest groups. There are 26 people in Class 3 and 1. Among them, 18 people participate in the calligraphy group, and 16 people participate in the chess group. How many people participate in both groups?
红光小学开设了两个兴趣小组，三1班有26人参加，其中18人参加书法小组，16人参加象棋小组，两个小组都参加的有多少人．
<gadget id="calculator">16 - 26</gadget>
<output>-10</output>

<gadget id="calculator">18 + (-10)</gadget>
<output>8</output>

<result>8</result>