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

long long curr, n, k, l, r, a[10001], d[10001];

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    cin>>n>>k;
    for(int i=0; i<n; i++) cin>>a[i], d[i] = 2e9;
    for(int i=0; i<n; i++) {
        curr = 0;
        l = max(i-k, 0LL);
        if(l) curr = d[l-1];
        r = min(i+k, n-1);
        d[r] = min(curr+a[i], d[r]);
    }
    cout<<d[n-1];
    return 0;
}