A group of people are arranged in a square matrix of n*n. There are 120 people in the outermost three floors. Find the value of n.
一群人排成n*n的方阵，最外3层共有120人，求n的数值．
<gadget id="calculator">120 / 4 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 + 3</gadget>
<output>13</output>

<result>13</result>