If the sum of the two sides of an isosceles triangle is 18 cm and one of the sides is 5 cm, what is the perimeter of the isosceles triangle in cm?
一个等腰三角形的两边之和是18厘米，其中一条边是5厘米，则这个等腰三角形的周长是多少厘米．
<gadget id="calculator">18 - 5</gadget>
<output>13</output>

<gadget id="calculator">13 + 13 + 5</gadget>
<output>31</output>

<result>31</result>