E. Two Round Dancestime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard outputOne day, n people (n is an even number) met on a plaza and made two round dances, each round dance consists of exactly \frac{n}{2} people. Your task is to find the number of ways n people can make two round dances if each round dance consists of exactly \frac{n}{2} people. Each person should belong to exactly one of these two round dances.Round dance is a dance circle consisting of 1 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 [1, 3, 4, 2], [4, 2, 1, 3] and [2, 1, 3, 4] are indistinguishable.For example, if n=2 then the number of ways is 1: one round dance consists of the first person and the second one of the second person.For example, if n=4 then the number of ways is 3. Possible options:  one round dance — [1,2], another — [3,4];  one round dance — [2,4], another — [3,1];  one round dance — [4,1], another — [3,2]. Your task is to find the number of ways n people can make two round dances if each round dance consists of exactly \frac{n}{2} people.InputThe input contains one integer n (2 \le n \le 20), n is an even number.OutputPrint one integer — the number of ways to make two round dances. It is guaranteed that the answer fits in the 64-bit integer data type.ExamplesInput2Output1Input4Output3Input8Output1260Input20Output12164510040883200
Input2
Output1
['combinatorics', 'math', '*1300']