//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define all(a) (a).begin(), (a).end()
using ll = long long;
const ll INF32 = 2e9;
const ll INF64 = 4e18;

void printYN(bool ok){
    if(ok)cout << "Yes" << endl;
    else cout << "No" << endl;
    return;
}

int main() {
    ll N,M;
    cin >> N >> M;
    vector<ll> A(N), B(N);
    rep(i, N)cin >> A[i];
    rep(i, N)cin >> B[i];
    ll now = 0, ans = 0;
    rep(i, M){
        if(A[i]>B[i])now += A[i]-B[i];
    }
    ans = now;
    rep(i,N-M){
        if(A[i]>B[i])now-=A[i]-B[i];
        if(A[i+M]>B[i+M])now+=A[i+M]-B[i+M];
        ans = max(ans, now);
    }
    cout << ans << endl;
    return 0;
}