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


int main() {
    int N, M; cin >> N >> M;
    vector<ll> A(N), B(N);
    vector<ll> C(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]) {
            C[i] = A[i] - B[i];
        } else {
            C[i] = 0;
        }
    }    
    
    ll ans = 0;
    ll cu = 0;
    for (int i = 0; i < M; i++) {
        cu += C[i];
    }
    ans = cu;
    for (int i = 0; i < N - M; i++) {
        
        cu -= C[i];
        cu += C[i+M];
        ans = max(ans, cu);
    }

    cout << ans << endl;

    return 0;
}