There are philatelists from 26 different countries who want to exchange the latest stamps issued by each country through correspondence. In order for each of these 26 people to have a set of the latest commemorative stamps of these 26 countries, how many letters should they communicate at least? letter.
有26个不同的国家的集邮爱好者，想通过互相通信的方法交换各国最新发行的邮票，为了使这26人每人都拥有这26个国家的一套最新纪念邮票，他们至少要通多少封信．
<gadget id="calculator">25 + 25</gadget>
<output>50</output>

<result>50</result>