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

public class Solution {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int a = scan.nextInt();
        int b = scan.nextInt();
        int[] c = new int[a];
        for(int i = 0; i < a; i++){
            c[i] = scan.nextInt();
        }
        int cost = 0;
        boolean check = true;
        int curind = 0;
        while(curind <= a -1){
            int min = Integer.MAX_VALUE;
            for(int j = 0; j <= b; j++){
                if(c[j] <= min){
                    min = c[j];
                    curind = j + b + 1;
                }
            }
            cost += min;
        }
        System.out.println(cost);
    }
}