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

typedef long long int lint;

int min(int a, int b) {
    if (a < b)
        return a;
    else
        return b;
}

struct Solution {
    lint total;
    int rightMostBulb;
};

class Solver {
public:
    Solver(int _n, int _k)
        : n(_n)
        , k(_k)
        , c(_n)
        , sol(_n) {
    }
    
    void read() {
        for (int i = 0; i < n; ++i)
            cin >> c[i];
    }
    
    void solve() {
        initSol();
        for (int i = 1; i < n; ++i)
            step(i);
        cout << sol[n-1].total << endl;
    }
    
private:
    
    void initSol()
    {
        cerr << "initSol " << c.size() << endl;
        
        lint val = c[0];
        int index = 0;
        for (int i = 1; i <= min(k,n); ++i) {
            cerr << i << endl;
            if (val > c[i]) {
                val = c[i];
                index = i;
            }
        }
        sol[0].total = val;
        sol[0].rightMostBulb = index;
    }
    
    lint getCost(int i)  {
        if (i < 0)
            return 0;
        else
            return sol[i].total;
    }
    
    void step(int m) {
        cerr << "step " << m << endl;
        
        int lastBulb = min(m + k, n-1);
        lint val = c[lastBulb];
        int index = lastBulb;
        lastBulb--;
        for (; lastBulb >= m - k; --lastBulb) {
            if (lastBulb < 0)
                break;
            if (val > c[lastBulb] + getCost(lastBulb - k - 1)) {
                val = c[lastBulb] + getCost(lastBulb - k - 1);
                index = lastBulb;
            }
        }
        sol[m].total = val;
        sol[m].rightMostBulb = index;
    }
    
    int n;
    int k;
    vector <int> c;
    vector<Solution> sol;
};

int main() {
     int n, k; cin >> n >> k;
    Solver s(n, k);
    s.read();
    s.solve();
    return 0;
}