Zhang Hua wanted to open up a rectangular space 4 meters long and 2 meters wide in his own rectangular courtyard as a small botanical garden, and built a fence around the space to prevent chickens and ducks from coming in and out. Please help him calculate how long the fence will be.
张华想在自家的长方形庭院内开辟一块长4米、宽2米的长方形空地作为小小植物园，并在这块空地的边上围一道篱笆，以防止鸡鸭出入．请你帮助他计算一下需要多长的篱笆．
<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<result>12</result>