The experimental primary school uses floor tiles to lay the floor of the computer room with a length of 90 decimeters and a width of 60 decimeters. From the perspective of not wasting materials, what is the longest side length of the selected square floor tiles?
实验小学用地板砖铺设长90分米、宽60分米的微机室地面，从不浪费材料的角度考虑，选择的正方形地板砖边长最长是多少分米？
<gadget id="calculator">2 * 3 * 5</gadget>
<output>30</output>

<result>30</result>