// 

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

using ll = long long;

#define rep(i, n) for (int i=0; i<(int)(n); ++(i))
#define rep3(i, m, n) for (int i=(m); (i)<(int)(n); ++(i))
#define repr(i, n) for (int i=(int)(n)-1; (i)>=0; --(i))
#define rep3r(i, m, n) for (int i=(int)(n)-1; (i)>=(int)(m); --(i))
#define all(x) (x).begin(), (x).end()

const ll LINF = (ll)(1e18);

ll op(ll a, ll b) { return max(a, b); }
ll e() { return -LINF; }
ll mapping(ll f, ll x) { return x + f; }
ll composition(ll f, ll g) { return f + g; }
ll id() { return 0LL; }

int main() {
	int n, k;
	cin >> n >> k;
	vector<int> a(n);
	rep(i, n) cin >> a[i];
	vector<ll> sum(n+1);
	rep(i, n) sum[i+1] = sum[i] + a[i];
	vector<ll> dp(n+1);
	lazy_segtree<ll, op, e, ll, mapping, composition, id> st(n+1);
	ll res = -LINF;
	dp[0] = 0;
	res = max(res, dp[0]);
	st.set(0, dp[0]);
	rep(i, n) {
		int li0 = max(0, (i+1)-(k-1)), li1 = max(0, (i+1)-k);
		dp[i+1] = st.prod(li1, i+1);
		res = max(res, st.prod(li0,i+1)+a[i]);
		st.apply(li0, i+1, a[i]);
		st.set(i+1, dp[i+1]);
	}
	res = max(res, dp[n]);
	cout << res << endl;
	return 0;
}