N,M = map(int, input().split())
a = list(map(int, input().split()))
b = list(map(int, input().split()))
s = 0
for i in range(M):
	if a[i] >= b[i]:
		s += a[i]-b[i]
ans = -1
ans = max(ans, s)
for i in range(N-M):
	e = i
	f = i+M
	if a[e] >= b[e]:
		s -= a[e]-b[e]
	if a[f] >= b[f]:
		s += a[f]-b[f]
	ans = max(ans, s)
	# print(s)
print(ans)