from collections import deque, defaultdict, Counter
from bisect import bisect_left, bisect_right, insort
from itertools import permutations, combinations, groupby
from heapq import heappop, heappush
import math, sys
input = lambda: sys.stdin.readline().rstrip("\r\n")
def printl(li, sep=" "): print(sep.join(map(str, li)))
def yn(flag): print(Yes if flag else No)
_int = lambda x: int(x)-1
MOD = 998244353 #10**9+7
INF = 1<<60
Yes, No = "Yes", "No"

N, M = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
C = [max(A[i]-B[i], 0) for i in range(N)]
cum = [0]
for c in C: cum.append(cum[-1]+c)

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