#include <stdio.h>
#include <iostream>//cin/cout
#include <string>//cout string
#include <functional>//rambda
#include <algorithm>
#include <iterator>//next/prev
#include <cmath>
#include <numeric>//iota
#include <vector>
#include <array>
#include <set>
#include <map>
#include <queue>

using namespace std;

using llong = long long;
const llong INF = 1LL << 60;//INF > 10^18(1e18)
const int INF32 = 1LL << 30;//INF32 > 10^9(1e9)
template <typename T> bool chmax(T& max, const T& b) {
	if (max >= b) return false;
	max = b;	return true;
}
template <typename T> bool chmin(T& min, const T& b) {
	if (min <= b) return false;
	min = b;	return true;
}
///////////////////ここまでtoolbox/////////////////////////////////////

int main() {
	int N, M;
	cin >> N >> M;
	vector<llong>A(N), B(N);
	for (int n = 0; n < N; n++) {
		cin >> A[n];
	}
	for (int n = 0; n < N; n++) {
		cin >> B[n];
	}
	//区間M日間で得する日だけ計上する
	llong ans = 0;
	llong temp = 0;
	for (int n = 0; n < M; n++) {
		if (A[n] - B[n] > 0) {
			temp += A[n] - B[n];
		}
	}
	ans = temp;
	for (int n = M; n < N; n++) {
		if (A[n - M] - B[n - M] > 0) {
			temp -= A[n - M] - B[n - M];
		}
		if (A[n] - B[n] > 0) {
			temp += A[n] - B[n];
		}
		chmax(ans, temp);
	}
	cout << ans << endl;
	return 0;
}