#if __has_include(<pch/all.h>)
#include <pch/all.h>
#else
#include <bits/stdc++.h>
#include <atcoder/all>
#endif

using namespace std;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
#define printYesNo(is_ok) puts(is_ok ? "Yes" : "No")
#define SORT(v) sort(v.begin(), v.end())
#define RSORT(v) sort(v.rbegin(), v.rend())
#define REVERSE(v) reverse(v.begin(), v.end())

template <typename Container>
void printVector(const Container &v, char delimiter = ' ')
{
    for (auto itr = v.begin(); itr != v.end(); itr++)
    {
        if (itr != v.begin())
        {
            cout << delimiter;
        }
        cout << *itr;
    }
    cout << endl;
}

template <typename Container>
void printlnVector(const Container &v)
{
    printVector(v, '\n');
}

void solve()
{
    int N, M;
    cin >> N >> M;

    vector<long long> v(N + 1);
    rep(i, N)
    {
        long long A;
        cin >> A;
        v[i + 1] += A;
    }

    rep(i, N)
    {
        long long B;
        cin >> B;
        v[i + 1] -= B;
    }

    rep(i, N)
    {
        v[i + 1] = max(v[i + 1], 0ll);
    }

    rep(i, N)
    {
        v[i + 1] += v[i];
    }

    long long ans = 0;
    rep(i, N - M + 1)
    {
        ans = max(ans, v[i + M] - v[i]);
    }
    cout << ans << endl;
}

int main()
{
    int T = 1;
    // cin >> T;

    while (T--)
    {
        solve();
    }

    return 0;
}