import java.util.Scanner;

public class Solution3 {


    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int k = scan.nextInt();
        int[] a = new int[n];
        for (int i = 0 ; i < n; i++)
            a[i] = scan.nextInt();
        int cost = 0, tcost;
        for (int i = 0 ; i <= k ; i++) {
            tcost = 0;
            for (int j = i; j < n; j += k + 1) {
                tcost += a[j];
            }
            if (tcost < cost || i == 0)
                cost = tcost;
        }
        System.out.println(cost);

    }


}