Couples in a Sauna
Source: 2013 Baltic Way, Problem 8
December 31, 2013
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Problem Statement
There are rooms in a sauna, each has unlimited capacity. No room may be attended by a female and a male simultaneously. Moreover, males want to share a room only with males that they don't know and females want to share a room only with females that they know. Find the biggest number such that any couples can visit the sauna at the same time, given that two males know each other if and only if their wives know each other.