import java.util.*;

public class Bulb {
    static int[] table;
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        int n,k,i;
        int[] cost;
        n = scan.nextInt();
        k = scan.nextInt();
        table = new int[n + 1];
        cost = new int[n+1];
        for(i=1;i<=n;i++){
            cost[i] = scan.nextInt();
        }
        
        	for(int l = 0; l < n + 1 ; l++){
        		table[l] = -1;
        	}
        int getResult = solve(cost, k, 0);
        System.out.println(getResult);
    }
    
    
    private static int solve(int[] cost, int k, int index){
    	if(index >= cost.length) return 0;
    	if(table[index] != -1) return table[index];
    	int minVal = Integer.MAX_VALUE;
    	for(int i = index; i < cost.length; i++){
    		int turnOff = solve(cost, k, index + k + 1) + cost[index];
    		minVal = Math.min(turnOff, minVal);
    	}
		table[index] = minVal;
    	return minVal;
    }
}