Please fill in four different numbers in the four boxes in the formula 1□*1□=1□*1□, so that the equal sign is established. Question: What is the sum of the four numbers filled in?
请在算式1□*1□=1□*1□，中的四个方框内填入四个互不相同的数码，使等号成立．问：所填的四个数码之和是多少？
<gadget id="calculator">2 + 5 + 0 + 8</gadget>
<output>15</output>

<result>15</result>