A key can only open one lock. Now there are 5 keys and 5 locks. How many trials must be done to ensure that all the keys and locks match?
一把钥匙只能开一把锁，现在有5把钥匙和5把锁，至少要试验多少次才一定能让所有的钥匙和锁相匹配？
<gadget id="calculator">4 + 3 + 2 + 1</gadget>
<output>10</output>

<result>10</result>