A total of 28 trees are planted from one end of a boulevard to the other. The distance between every two adjacent trees is 4 meters. How long is this boulevard in meters?
从一条林荫道的一端到另一端共栽了28棵树，每相邻的两棵树之间相隔4米，这条林荫道长多少米？
<gadget id="calculator">28 - 1</gadget>
<output>27</output>

<gadget id="calculator">27 * 4</gadget>
<output>108</output>

<result>108</result>