#include <bits/stdc++.h>
using namespace std;

const int MAXN = 10001;
const int MAXK = 1000;
const long long INF = 1ll << 50;

long long dp[MAXN];

void solve(){
	int n, k;
	cin >> n >> k;

	dp[0] = 0;
	for (int i = 1; i <= n; i++) {
		dp[i] = INF;
	}
	for (int i = 1; i <= n; i++) {
		long long c;
		cin >> c;
		int next = min(n, i + k);
		int prev = max(0, i - k - 1);
		dp[next] = min(dp[next], dp[prev] + c);
	}
	cout << dp[n];
}

int main(){
	int t = 1;
	while (t--) {
		solve();
		cout << endl;
	}
}