#include <bits/stdc++.h>
using namespace std;

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return vector(arg, init);
    else return vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename Container>
auto distance(const Container &c, decltype(begin(c)) iter) {
    return distance(begin(c), iter);
}

template <typename RIter, typename Compare = less<typename iterator_traits<RIter>::value_type>>
auto isort(RIter first, RIter last, Compare comp = Compare()) {
    vector<int> i(distance(first, last));
    iota(begin(i), end(i), 0);
    sort(begin(i), end(i), [&](auto x, auto y) {
        return comp(*(first + x), *(first + y));
    });
    return i;
}

template <typename, template <typename> typename, typename = void_t<>>
struct detect : false_type {};
template <typename T, template <typename> typename Check>
struct detect<T, Check, void_t<Check<T>>> : true_type {};
template <typename T, template <typename> typename Check>
constexpr inline bool detect_v = detect<T, Check>::value;

template <typename T>
using has_member_sort = decltype(declval<T>().sort());

template <typename Container, typename Compare = less<typename Container::value_type>>
auto sorted(Container c, Compare comp = Compare()) {
    if constexpr (detect_v<Container, has_member_sort>) {
        c.sort(comp);
        return c;
    }
    else {
        sort(begin(c), end(c), comp);
        return c;
    }
}

template <typename Container, typename Compare = equal_to<typename Container::value_type>>
auto uniqued(Container c, Compare comp = Compare()) {
    c.erase(unique(begin(c), end(c), comp), end(c));
    return c;
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

#include <atcoder/lazysegtree>

auto op(int64_t a, int64_t b) {
    return max(a, b);
}
auto elem() {
    return INT64_MIN;
}

auto mapping(int64_t f, int64_t x) {
    return f + x;
}
auto composition(int64_t f, int64_t g) {
    return f + g;
}
auto id() {
    return int64_t(0);
}

using segtree = atcoder::lazy_segtree<int64_t, op, elem, int64_t, mapping, composition, id>;

int main() {
    int n, k; cin >> n >> k;
    auto a = vec<int64_t>(uns, n);
    for (auto &e : a) cin >> e;

    auto dp = vec<int64_t>(uns, n + 1);

    segtree seg(vec<int64_t>(0, n + k + 1));

    dp[0] = 0;
    for (int i = 1; i <= n; ++i) {
        int l = i - k;
        int r = i - 1;

        seg.apply(l + k, r + k, a[i - 1]);

        dp[i] = max(
            dp[i - 1],
            seg.prod(l + k, r + k)
        );

        seg.set(i + k, dp[i]);
    }

    cout << dp[n] << endl;
}