There are 23 buttons, 4 coats are buttoned, 5 are nailed to each coat, how many buttons are left?
有23颗扣子，给4件上衣钉扣子，每件上衣钉5颗，还剩多少颗？
<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">23 - 20</gadget>
<output>3</output>

<result>3</result>