N, M = (int(x) for x in input().split())
A = [int(x) for x in input().split()]
B = [int(x) for x in input().split()]
pfx = [0] * (N + 1)
for i in range(N):
    pfx[i + 1] = pfx[i] + max(A[i] - B[i], 0)
print(max(pfx[i + M] - pfx[i] for i in range(N - M + 1)))