def main():
    N, M = map(int, input().split())
    A = list(map(int ,input().split()))
    B = list(map(int, input().split()))

    gains = []
    for i in range(N):
        d = A[i] - B[i]
        if d > 0:
            gains.append((d, i))
    if len(gains) == 0:
        print(0)
        return

    answer = 0
    left = 0
    right = 0
    ans = gains[left][0]
    while left < len(gains):
        while right < len(gains) - 1 and gains[right + 1][1] < gains[left][1] + M:
            ans += gains[right + 1][0]
            right += 1

        answer = max(answer, ans)
        if left < right:
            ans -= gains[left][0]
            left += 1
        else:
            if right < len(gains) - 1:
                left += 1
                right += 1
                ans = gains[left][0]
            else:
                break
    print(answer)
        



if __name__ == "__main__":
    main()
#    main2()