#!/usr/bin/env python3
# -*- coding: utf-8-auto -*-

N, M = map(int, input().split())
A_list = list(map(int, input().split()))
B_list = list(map(int, input().split()))

temp_list = [max(x[0]-x[1],0) for x in zip(A_list, B_list)]



temp = sum(temp_list[:M])
max_value = temp

for i in range(N-M+1):
    if i == 0:
        continue
    # print(i, i+M-1)
    # print(temp_list[i:i+M])
    temp = temp - temp_list[i-1] + temp_list[i+M-1]
    max_value = max(max_value, temp)
print(max_value)