#include <bits/stdc++.h>
using namespace std;
// #include <atcoder/modint>
// using namespace atcoder;
// using mint = modint998244353;
using ll = long long;
#define fix(x) fixed << setprecision(x)
#define rep(i, n) for(int i = 0; i < n; ++i)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL << 62), MOD = 998244353;
constexpr int INF = (1 << 30);

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n,m;
    cin >> n >> m;
    ll ans = 0;
    vector<ll> x(n+1,0), a(n,0), b(n,0);
    rep(i,n) cin >> a[i];
    rep(i,n) cin >> b[i];
    rep(i,n) x[i+1] = x[i] + max(a[i]-b[i],0LL);
    rep(i,n-m+1) chmax(ans,x[i+m]-x[i]);
    cout << ans << '\n';
    return 0;
}