# Write a function to find n-th rencontres number.
def binomial_coeffi(n, k):
    if k == 0 or k == n:
        return 1
    return binomial_coeffi(n - 1, k - 1) + binomial_coeffi(n - 1, k)


def rencontres_number(n, m):
    if n == 0 and m == 0:
        return 1
    if n == 1 and m == 0:
        return 0
    if m == 0:
        return (n - 1) * (rencontres_number(n - 1, 0) + rencontres_number(n - 2, 0))
    return binomial_coeffi(n, m) * rencontres_number(n - m, 0)
