from itertools import accumulate
def main():
	n, k, *a = map(int, open(0).read().split())
	p = [x if x > 0 else 0 for x in a]
	acc = [0] + list(accumulate(a))
	p_acc = [0] + list(accumulate(p))
	rev_p_acc = [0] + list(accumulate(p[::-1]))
	print(max(max(0, acc[k + i] - acc[i]) + p_acc[i] + rev_p_acc[n - k - i] for i in range(n - k + 1)))
	
if __name__=="__main__":
	main()