#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (ll i = 0; i < (n); i++)

int main() {
    ll n, m;
    cin >> n >> m;
    vector<ll> A(n), B(n), S(n+1);
    rep(i, n) cin >> A[i];
    rep(i, n) cin >> B[i];
    rep(i, n) S[i+1] = S[i] + max(0LL, A[i] - B[i]);
    ll ans = S[m] - S[0];
    rep(i, n-m+1) ans = max(ans, S[i+m] - S[i]);
    cout << ans << endl;
    return 0;
}