#include <bits/stdc++.h>
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define all(c) (c).begin(), (c).end()
#define sqr(x) (x)*(x)
#define fname ""

using namespace std;

typedef long long ll;
const double eps = 1e-9;
const double PI = acos(-1.0);
const int inf = int (1e9+7);
const ll INF = (ll) 8e18+7;
const int mod = int (1e9+7);     
const int N = int (2e5+7);    

int n, k, a[N];
ll dp[N], t[N];

void build(int v, int tl, int tr) {
	if(tl == tr) {
		t[v] = dp[tl];
		return;
	}
	int tm = (tl + tr) >> 1;
	build(v + v, tl, tm);
	build(v + v + 1, tm + 1, tr);
	t[v] = min(t[v + v], t[v + v + 1]);
}

void upd(int v, int tl, int tr, int pos, ll val) {
	if(tl == tr) {
		t[v] = val;
		return;
	}
	int tm = (tl + tr) >> 1;
	if(pos <= tm)
		upd(v + v, tl, tm, pos, val);
	else
		upd(v + v + 1, tm + 1, tr, pos, val);
	t[v] = min(t[v + v], t[v + v + 1]);
}

ll get(int v, int tl, int tr, int l, int r) {
	if(r < tl || tr < l)
		return INF;
	if(l <= tl && tr <= r)
		return t[v];
	int tm = (tl + tr) >> 1;
	return min(get(v + v, tl, tm, l, r),
				get(v + v + 1, tm + 1, tr, l, r));
}

int main () { 
   	//freopen(fname".in", "r", stdin);
   	//freopen(fname".out", "w", stdout);
   	ios_base::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n >> k;
	dp[0] = 0;
	for(int i = 1; i <= n; i ++)
		dp[i] = INF;
	for(int i = 1; i <= n; i ++)
		cin >> a[i];
	for(int i = 1; i <= n; i ++) {
		dp[min(n, i + k)] = min(dp[min(n, i + k)], dp[max(0, i - k - 1)] + a[i]);
	}
	cout << dp[n] << endl;
	return 0;
}