import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int k = in.nextInt();

        PriorityQueue<Bulb> bulbs = new PriorityQueue<>();
        Map<Integer, Bulb> map = new HashMap<>();
        for (int i=0; i < n; i++) {
            long c = in.nextLong();
            Bulb bulb = new Bulb();
            bulb.index = i;
            bulb.cost = c;
            bulbs.add(bulb);
            map.put(i, bulb);
        }

        int sum = 0;

        while (!bulbs.isEmpty()) {
            Bulb bulb = bulbs.poll();
            sum += bulb.cost;
            for (int i = Math.max(0, bulb.index - k); i < Math.min(n, bulb.index + k + 1); i++) {
                Bulb b = map.get(i);
                bulbs.remove(b);
            }
        }
        System.out.println(sum);

    }

    static class Bulb implements Comparable<Bulb> {
        int index;
        long cost;

        @Override
        public int compareTo(Bulb o) {
            if (cost == o.cost)
                return 0;
            return Math.abs((int) (cost - o.cost));
        }
    }
}