#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vll = vector<ll>;
template <typename K, typename V>
using umap = unordered_map<K, V>;

#define rep(i, n) for (int i = 0; i < n;i++)
#define rep1(i, n) for (int i = 1; i <= n;i++)
#define rrep(i, n) for (int i = n - 1; i >= 0;i--)
#define rrep1(i, n) for (int i = n; i >= 1;i--)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define INF 1LL << 60
#define chmin(a, b) a = min(a, b)
#define chmax(a, b) a = max(a, b)

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, m;
    cin >> n >> m;
    vector<ll> a(n), b(n);
    rep(i, n) {
        cin >> a[i];
    }
    rep(i, n) {
        cin >> b[i];
    }
    vector<bool> cancel(n);
    ll sum = 0;
    rep(i, m) {
        if (a[i] < b[i]) {
            cancel[i] = true;
        } else {
            sum += a[i] - b[i];
        }
    }
    ll ans = sum;
    for (int i = m; i < n;i++) {
        if (a[i] < b[i]) {
            cancel[i] = true;
        } else {
            sum += a[i] - b[i];
        }
        if (!cancel[i - m]) {
            sum -= a[i - m] - b[i - m];
        }
        chmax(ans, sum);
    }
    cout << ans << endl;
}