import sys
from itertools import accumulate
from typing import List, Tuple

MOD = 998244353

int1 = lambda x: int(x) - 1
input = lambda: sys.stdin.readline().rstrip('\n')
ii = lambda: int(input())
vi = lambda: list(map(int, input().split()))
vi1 = lambda: list(map(int1, input().split()))


def dbg(*args, **kwargs):
    print(*(repr(arg) for arg in args), *(f'{k}: {repr(v)}' for k, v in kwargs.items()),
          sep='; ', file=sys.stderr, flush=True)


def main():
    n, m = vi()
    a = vi()
    b = vi()
    c = [max(0, a[i] - b[i]) for i in range(n)]
    s = [0] + list(accumulate(c))
    z = 0
    for i in range(n - m + 1):
        z = max(z, s[i + m] - s[i])
    return z


def _start():
    if (ret := main()) is not None:
        print(*ret) if isinstance(ret, List) or isinstance(ret, Tuple) else print(ret)


if __name__ == '__main__':
    _start()