#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using pii = pair<int, int>;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define repr(i, n) for (int i = (int)(n - 1); i >= 0; --i)

ll op(ll x, ll y) { return max(x, y); }
ll e() { return 0; }
ll mapping(ll f, ll x) { return f + x; }
ll composition(ll f, ll g) { return f + g; }
ll id() { return 0; }

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n, K;
    cin >> n >> K;
    vi a(n);
    rep(i, n) cin >> a[i];
    lazy_segtree<ll, op, e, ll, mapping, composition, id> seg(n + 1);
    rep(i, n) {
        seg.apply(i + 1, seg.prod(max(0, i + 1 - K), i + 1));
        seg.apply(0, i + 1, a[i]);
    }
    ll ret = seg.prod(n - K + 1, n + 1);
    cout << ret << endl;
    return 0;
}