Uncle Li got a new house. The new house has 4 rooms and 4 keys. He knows that each key can only open one door, but he doesn’t know which key will open which door. Now he wants to open all the 4 closed rooms. door, how many times should he at least try to open it?
李叔叔拿到了新房，新房有4个房间，也有4把钥匙，他知道每把钥匙只能开一个房门，但不知道哪把钥匙开哪一个房门，现在要打开所有关闭的4个房门，那么他至少要试开多少次？
<gadget id="calculator">3 + 2 + 1</gadget>
<output>6</output>

<result>6</result>