Uncle Wang wants to use a fence to build a rectangular open space 15 meters long and 8 meters wide against the wall. Please help him calculate the minimum required fence? (There is no fence on the side next to the wall)
王大伯要靠墙用篱笆一个长15米，宽8米的长方形空地．请帮他算一算最少需多少的篱笆？(靠墙的一面不用篱笆)
<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<gadget id="calculator">16 + 15</gadget>
<output>31</output>

<result>31</result>