A piece of triangular land, the lengths of the three sides are 18, 27, and 39 respectively. Trees should be planted on all three sides of it, including three vertices. It is required that every two adjacent trees are equally spaced. How many trees can be planted at least? Tree.
一块三角形土地，3条边的长度分别是18、27、39，要给它的3条边上都植上树，包括3个顶点，要求相邻每2棵树间距相等，最少可以植多少棵树．
<gadget id="calculator">18 + 27 + 39</gadget>
<output>84</output>

<gadget id="calculator">84 / 3</gadget>
<output>28</output>

<result>28</result>