#!/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)]

max_value = 0

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