#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int i, n, k; cin >> n >> k;
    vector <long long> c;    
    vector <long long> best;
    vector<vector<long long>> besti;
    for (i = 0; i < n; i++){
        long long t; cin >> t;
        c.push_back(t);
    }
    
    for (i = 0; i < n; i++){
        vector<long long> answer;
        int opt = -1;
        for (int j = (-1)*k; j <= k; j++){
            if (i + j < 0) answer.push_back(-1);
            else if (i + j >= n) answer.push_back(-1);                
            else{
                if (i == 0){
                    answer.push_back(c[i+j]);
                    if (opt == -1 || opt > c[i+j]) opt = c[i+j];
                }
                else{
                    if (j != k){
                        answer.push_back(besti[i-1][j+k+1]);
                        if (opt == -1 || opt > besti[i-1][j+k+1]) opt = besti[i-1][j+k+1];
                    }
                    else{
                        answer.push_back(best[i-1]+c[i+j]);
                        if (opt == -1 || opt > best[i-1]+c[i+j]) opt = best[i-1]+c[i+j];                        
                    }
                }
            }
        }
        besti.push_back(answer);
        best.push_back(opt);
    }
            
    
    
    cout << best[n-1];
    
    
    
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    return 0;
}