N, M = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
acc = 0
ret = 0

for i in range(M-1):
    acc += max(A[i]-B[i], 0)

for i in range(M-1, N):
    acc += max(A[i]-B[i], 0)
    # print(acc)
    ret = max(ret, acc)
    acc -= max(A[i-(M-1)]-B[i-(M-1)], 0)


print(ret)