/* -*- coding: utf-8 -*-
 *
 * 3684.cc:  No.3684 chokudai_niku.png - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 200000;

/* typedef */

using ll = long long;

/* global variables */

int as[MAX_N], bs[MAX_N];
ll dss[MAX_N + 1];

/* subroutines */

/* main */

int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) scanf("%d", as + i);
  for (int i = 0; i < n; i++) scanf("%d", bs + i);

  for (int i = 0; i < n; i++) dss[i + 1] = dss[i] + max(0, as[i] - bs[i]);

  ll maxd = 0;
  for (int i = 0; i + m <= n; i++)
    maxd = max(maxd, dss[i + m] - dss[i]);

  printf("%lld\n", maxd);
  
  return 0;
}