#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for (ll i = a; i < b; i++)
using ll = long long;

int main(){
    int n, m;
    cin >> n >> m;
    vector<ll> a(n), b(n), c(n), s(n + 1);
    rep(i, 0, n) cin >> a[i];
    rep(i, 0, n) cin >> b[i];
    rep(i, 0, n) c[i] = max(0LL, a[i]- b[i]);
    rep(i, 0, n) s[i + 1] = s[i] + c[i]; 
    ll ans = 0;
    rep(i, 0, n) {
        if(i + m > n) break;
        ans = max(ans, s[i + m] - s[i]);
     }
    cout << ans << endl;
}