while 1:
	n,k = map(int,raw_input().split())
	if n == 0: break
	c = [int(raw_input()) for i in range(n)]
	Ck1 = 1
	for i in range(k):
		Ck1 *= c[i]
	Ck = Ck1*max(c[k:])/min(c[:k]) if k < n else Ck1
	cur1 = Ck1
	for i in range(k,n):
		cur1 = cur1*c[i]/c[i-k]
		cur2 = cur1*max(c[:i-k+1]+c[i+1:])/min(c[i-k+1:i+1])
		Ck1 = max(Ck1,cur1)
		CK = max(Ck,cur2)
	if n-k >= 2: Ck = max(Ck1,Ck)
	print Ck-Ck1 if Ck-Ck1 >= 0 else "NO GAME"	