from itertools import accumulate

N, M = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
acc = list(accumulate(map(lambda x: max(x[0] - x[1], 0), zip(A, B)), initial=0))

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