#include <iostream>
#include <algorithm>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
//#define endl "\n";
int main(){
    ll N, M;
    cin >> N >> M;
    vector<ll> A(N), B(N);
    for(int i = 0; i < N; i++) cin >> A[i];
    for(int i = 0; i < N; i++) cin >> B[i];
    ll sum = 0;
    for(int i = 0; i < M; i++){
        if(A[i] - B[i] > 0) sum += A[i] - B[i];
    }
    ll ans = sum;
    for(int i = M; i < N; i++){
        if(A[i - M] - B[i - M] > 0){
            sum -= A[i - M] - B[i - M];
        }
        if(A[i] - B[i] > 0){
            sum += A[i] - B[i];
        }
        ans = max(ans, sum);
    }
    cout << ans << endl;
    return 0;
}