On Arbor Day, the students planted trees, divided into 15 or 18 people in each group, and all of them could be divided exactly. At least how many people participated in the tree planting activities.
植树节，同学们去种树，按每组15人或18人分，都能正好分完，参加植树活动的至少有多少人．
<gadget id="calculator">3 * 5 * 2 * 3</gadget>
<output>90</output>

<result>90</result>