import sys
import math
import bisect
import heapq
from collections import deque, defaultdict 
#160427717982164055zq
# -------------------------------------------------
def ST(): return input().rstrip()
def IN(): return int(input())
def ML(typ=int): return [typ(x) for x in input().split()]
def IM(): return ML()
def IL(): return ML()
def SR(n:int)->list: return [input().rstrip() for _ in range(n)]
def IMatrix(n:int)->list: return [Mul(int) for _ in range(n)]

def prefix_sum(L): #1次元リストの累積和を返す
    ret = [L[0]]
    for i in range(1, len(L)):
        ret.append(ret[i-1]+L[i])
    return ret
    
N, M = IM()
A = [0]+IL()
B = [0]+IL()
for i in range(1, N+1):
	if A[i] < B[i]:
		A[i] = 0
		B[i] = 0
#print(A, B)

pA = prefix_sum(A)
pB = prefix_sum(B)
ans = 0
for i in range(N-M+1):
	ans = max(ans, pA[i+M]-pA[i]+pB[i]-pB[i+M])

print(ans)