There are 35 students lined up in a horizontal line. Xiaohong is the 21st from the left, and Xiaojun is the 20th from the right. How many students are there between Xiaohong and Xiaojun?
有35个同学排成一列横队，从左边数起小红是第21名，从右边数起小军是第20名，小红和小军中间隔着多少位同学．
<gadget id="calculator">20 - 35 - 2</gadget>
<output>-17</output>

<gadget id="calculator">21 + (-17)</gadget>
<output>4</output>

<result>4</result>