The new administrator of the teaching building took 15 different keys to open 15 classrooms, but he didn't know which key opened which door, and how many times he tried to open at most, he could pair the key with the classroom door lock.
新来的教学楼管理员拿15把不同的钥匙去开15个教室的站，但是不知哪一把钥匙开哪一个门，他最多试开多少次，就可将钥匙与教室门锁配对．
<gadget id="calculator">15 - 1</gadget>
<output>14</output>

<gadget id="calculator">14 + 1</gadget>
<output>15</output>

<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<gadget id="calculator">15 * 7</gadget>
<output>105</output>

<result>105</result>