One day people ( is even) met on a plaza and made two round dances. Find the number of ways people can make two round dances if each round dance consists of exactly people. Each person should belong to exactly one of these two round dances.
Round dance is a dance circle consisting of or more people. Two round dances are indistinguishable (equal) if one can be transformed to another by choosing the first participant. For example, round dances and are indistinguishable.
One even integer .
Print the number of ways to make two round dances. It is guaranteed that the answer fits in the -bit integer data type.
For example, for the number of ways is :
one round dance — , another — ;
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