The 35 students in the class are lined up in a row, the monitor is ranked 20th from the left, and the deputy monitor is ranked 21st from the right. How many other students are separated between the monitor and the deputy monitor.
全班35个同学排成一排，班长排在从左边数的第20位，副班长排在从右边数的第21位．班长和副班长中间隔着多少名其他同学．
<gadget id="calculator">20 - 35 - 2</gadget>
<output>-17</output>

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

<result>4</result>