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

typedef long long LL;
const int MAXN = 1e6 + 10;
const LL MOD = 1e9 + 7;
const LL INF = 1e17;

LL A[MAXN];
LL debot[MAXN];
LL ans[MAXN];
bool comp(pair<LL, LL> a, pair<LL, LL> b){
    return a.first < b.first;
}
int main(){
    int N, K;
    cin >> N >> K;
    for(int i = 1;i <= N;++i){
        cin >> A[i];
    }
    vector<pair<LL, LL> > heapK;
    vector<pair<LL, LL> > heap2K;
    ans[0] = INF;
    for(int i = 1;i <= N;++i){
        while((!heapK.empty()) && heapK[0].second < i - K){
            pop_heap(heapK.begin(), heapK.end(), comp);
            heapK.pop_back();
        }
        while((!heap2K.empty()) && heap2K[0].second < (i - (2 * K + 1))){
            pop_heap(heap2K.begin(), heap2K.end(), comp);
            heap2K.pop_back();
        }
        debot[i] = A[i] + (i <= K + 1?0:heap2K[0].first);
        heapK.push_back(make_pair(debot[i], i));
        heap2K.push_back(make_pair(debot[i], i));
        push_heap(heap2K.begin(), heap2K.end(), comp);
        push_heap(heap2K.begin(), heap2K.end(), comp);
        ans[i] = heapK[0].first;
        ans[i] = min(ans[i], debot[i]);
    }
    cout << ans[N] << "\n";
	return 0;
}