def stirling(n, k):
	if k == 1:
		return 1
	if k == 0:
		return 0
	if n == k:
		return 1
	if k > n:
		return 0

	return k * stirling(n - 1, k) + stirling(n - 1, k - 1)

n = 7
k = 4
print(stirling(n, k))