#include <bits/stdc++.h>
#define endl '\n'
using namespace std;
using ll = long long;

void solve() {
    ll N, M;
    cin >> N >> M;
    vector<ll> A(N), B(N);
    for (int i = 0; i < N; i++) cin >> A[i];
    for (int i = 0; i < N; i++) cin >> B[i];

    for (int i = 0; i < N; i++) {
        if (A[i] < B[i]) {
            A[i] = 0;
            B[i] = 0;
        }
    }

    vector<ll> a(N+1, 0), b(N+1, 0);
    for (int i = 1; i <= N; i++) a[i] += a[i-1] + A[i-1];
    for (int i = 1; i <= N; i++) b[i] += b[i-1] + B[i-1];

    ll ans = 0;
    for (int i = M; i <= N; i++) {
        ans = max(ans, (a[i] - a[i-M]) - (b[i] - b[i-M]));
    }

    cout << ans << endl;
    return;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    ll T = 1;
    // cin >> T;
    while (T--) {
        solve();
    }
    return 0;
}