To fix a square picture frame to the wall, 5 nails are used on each side. What is the minimum number of nails needed?
要把正方形的画框固定在墙上，每边用5个钉子，最少要用多少个钉子？
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<result>16</result>