#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, a, b) for (int i = (a); i < (int)(b); i++)
#define all(x) x.begin(), x.end()

template <typename T>
inline bool chmax(T& a, const T& b) {
    return ((a < b) ? (a = b, true) : (false));
}

void solve() {
    int N, M;
    cin >> N >> M;
    vector<int> A(N);
    rep(i, 0, N) cin >> A[i];
    vector<ll> sum(N + 1);
    rep(i, 0, N) {
        sum[i + 1] = sum[i] + (A[i] >= 0 ? A[i] : 0);
    }
    ll ans = -1e18;
    rep(l, 0, N) {
        int r = l + M;
        if (r > N) break;
        chmax(ans, sum[r] - sum[l]);
    }

    cout << ans << '\n';
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int T = 1;
    // cin >> T;
    while (T--) {
        solve();
    }
}