import itertools
from functools import cache
import sys
from itertools import accumulate

sys.setrecursionlimit(10 ** 9)
import math
from collections import Counter, deque
input = lambda: sys.stdin.readline().rstrip()
mod = 998244353

n, m = map(int, input().split())
a = list(map(int, input().split()))
b = list(map(int, input().split()))

toku = list()

for i in range(n):
    if a[i] - b[i] < 0:
        toku.append(0)
    else:
        toku.append(a[i] - b[i])

# print(toku)
toku_acc = [0] + list(accumulate(toku))
# print(toku_acc)

ans = 0
for i in range(1, n - m + 2):
    # print(i)
    temp_toku = toku_acc[i + m - 1] - toku_acc[i - 1]
    ans = max(ans, temp_toku)
print(ans)