One key opens one lock. There are 5 keys and 5 locks. What is the minimum number of trials required to make all the keys and locks match each other?
一把钥匙开一把锁，现有5把钥匙5把锁，最少要试验多少次才能使全部的钥匙和锁相互匹配．
<gadget id="calculator">1 + 1 + 1 + 1</gadget>
<output>4</output>

<result>4</result>