There are two types of elves on the Alpha spaceship. One type of elves always lie and one type of elves never lie. Each elf knows what type the other elves are. A group of elves held a party on Monday. Tell what type the other elves are, and all the elves say "liar" 420 times in total. The group of elves held the same meeting again on Thursday, but one elf was absent. This time all the elves said "liar" 390 times in total. Then how many elves are there in total at the meeting on Monday?
阿尔法飞船上有两类精灵，一类精灵总是说谎，一类精灵从不说谎，每个精灵都知道其他精灵分别是什么类型，有一群精灵在星期一举行了一次聚会，每个精灵都要说出其他精灵分是什么类型，全部精灵总共说了420次"说谎者"．这群精灵在星期四又举行了一次相同的聚会，但有一个精灵缺席，这次全部精灵总共说了390次"说谎者"．则参加星期一聚会的精灵总共有多少个．
<gadget id="calculator">14 + 15</gadget>
<output>29</output>

<result>29</result>