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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    long n,k;
    cin >> n >> k;
    
    vector<long> ws;    
    for (long i=0;i<n;i++){
        long t;
        cin >> t;
        ws.push_back(t);
    }
    
    long a[n]; // best cost of turning off all bulbs below i
    
    for (long i=0;i<n;i++)
        a[i] = std::numeric_limits<long>::max();
    
    for (long i=0;i<n;i++){ // add each bulb
        long lower = i-k; // first bulb that lit by i
        long upper = min(n-1,i+k); // last bulb lit by i
        
        long cost = ws[i];
        if (lower > 0) // there are unlit bulbs
            cost += a[lower-1]; // light up all bulbs up to lower
        
        // update each bulb affected by i
        for (long j=max(0L,lower); j<=upper; j++)
            a[j] = min(a[j],cost);
    }
    cout << a[n-1] << endl;
    
    return 0;
}