N, M = map(int, input().split())
a_list = list(map(int, input().split()))
b_list = list(map(int, input().split()))

c_list = []

for n in range(N):
    a = a_list[n]
    b = b_list[n]
    c_list.append(max(0, a - b))

res = 0
for m in range(M):
    res += c_list[m]

now = res
for n in range(N - M):
    now -= c_list[n]
    now += c_list[n + M]
    res = max(res, now)

print(res)