There are 45 students in Class A of the fourth grade, 35 of them subscribe to "Primary School Mathematics Newspaper", and 30 people subscribe to "Youth Daily". Each person subscribes at least one copy. How many people subscribe to both newspapers?
四年级甲班有45人，其中有35人订阅《小学数学报》，有30人订阅《少年报》，每人至少订一份，两种报都订的有多少人？
<gadget id="calculator">30 - 45</gadget>
<output>-15</output>

<gadget id="calculator">35 + (-15)</gadget>
<output>20</output>

<result>20</result>