There are 40 students in class 31, 25 of them have subscribed to "One Thousand and Zero Nights", 23 have subscribed to "Aesop's Fables", and 19 have subscribed to both publications. So how many people don't subscribe to either publication?
三1班有40名同学，其中25人订阅了《一千零夜》，23人订阅了《伊索寓言》，有19人两种刊物都订阅了．那么，有多少人两种刊物都没有订阅？
<gadget id="calculator">23 - 19</gadget>
<output>4</output>

<gadget id="calculator">25 + 4</gadget>
<output>29</output>

<gadget id="calculator">40 - 29</gadget>
<output>11</output>

<result>11</result>