#include <iostream>
#include <limits>
#include <vector>

#include <atcoder/lazysegtree>

long long op(long long x, long long y) {
    return std::max(x, y);
}
long long e() {
    return std::numeric_limits<long long>::min();
}
long long mapping(long long f, long long x) {
    return f + x;
}
long long composition(long long f, long long g) {
    return f + g;
}
long long id() {
    return 0;
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int n, k;
    std::cin >> n >> k;

    std::vector<long long> a(n);
    for (auto &e : a) std::cin >> e;

    atcoder::lazy_segtree<long long, op, e, long long, mapping, composition, id> seg(n + 1);
    seg.set(n, 0);

    for (int i = 0; i < n; ++i) {
        seg.set(n - i - 1, seg.all_prod());
        seg.apply(n - i, std::min(n + 1, n - i + k - 1), a[i]);
    }

    std::cout << seg.all_prod() << std::endl;
}