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

public class Solution {

    static int[] c;
    static int k;
    static long[][] dp;
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n;
        n = in.nextInt();
        k = in.nextInt();
   
        dp = new long[n+1][n+1];
        for(int i=0; i<=n; i++){
            Arrays.fill(dp[i], -2);
        }
        c = new int[n];
        for(int i=0; i<n; i++) c[i] = in.nextInt();
        
        long ans=(long)1e15;
        for(int i=0; i<=k; i++){
            ans=Math.min(ans, c[i]+solve(i+k+1, i));
            //System.out.println(ans);
        }
        System.out.println(ans);
    }
    
    public static long solve(int i, int last){
        if (i-last>2*k+1) {return (long)1e15;}
        if (i>=c.length){
            return 0;
        }
        
        if (dp[i][last]!=-2) return dp[i][last];
        if (i-last==2*k+1){
            return dp[i][last]=c[i]+solve(i+1,i);
        }
        return dp[i][last]=Math.min(solve(i+k+1, last), c[i]+solve(i+1, i));
        
    }
}