// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
#include<atcoder/lazysegtree>
using namespace std;
using namespace atcoder;
using ll = long long;
const ll inf = 1LL << 60;

using S = ll;
S op(S l, S r){
	return max(l, r);
}
S e(){
	return -inf;
}
using F = ll;
S mapping(F f, S x){
	return f + x;
}
F composition(F l, F r){
	return l + r;
}
F id(){
	return 0;
}

void solve(){    
    int n, k;
	cin >> n >> k;
	vector<ll> A(n);
	for(auto &a : A) cin >> a;
	lazy_segtree<S, op, e, F, mapping, composition, id> seg(n + 1);
	seg.set(0, 0);
	for(int i = 1; i <= n; i++){
		ll a = A[i - 1];
		seg.set(i, seg.prod(0, i));
		seg.apply(max(0, i - k + 1), i, a);
	}
	cout << seg.all_prod() << endl;
}

int main(){
    cin.tie(0)->sync_with_stdio(0);
    int t;
    t = 1;
    // cin >> t;
    while(t--) solve();
}