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

int main() {

    ll N,M;
    cin >> N >> M;
    vector<ll> A(N);
    vector<ll> B(N);
    vector<ll> pre(N+1,0);
    for(ll i = 0;i<N;i++){
        cin >> A[i];
    }
    for(ll i = 0;i<N;i++){
        cin >> B[i];
        pre[i+1] = pre[i] + max(A[i]-B[i],0LL);
    }
    ll ans = 0;
    for(ll i = 0;i+M<N+1;i++){
        ans = max(ans,pre[i+M] - pre[i]);
    }
    cout << ans << endl;

}