#include <algorithm>
#include <array>
#include <chrono>
#include <climits>
#include <cmath>
#include <cstdlib>
#include <deque>
#include <forward_list>
#include <functional>
#include <iostream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <regex>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <valarray>
#include <vector>

using namespace std;

int n, k;
vector<long long> costs;

long long bruteforce(int bulb)
{
	if (bulb >= costs.size())
		return 0;

	long long minCost = INT_MAX;
	for (int i = max(bulb - k, 0); i <= min(n - 1, bulb + k); i++)
	{
		long long cost = costs[i] + bruteforce(i + k + 1);
		if (cost < minCost)
			minCost = cost;
	}
	return minCost;
}

int main()
{
	ios::sync_with_stdio(false);

	cin >> n >> k;

	costs.resize(n);
	for (int i = 0; i < n; i++)
		cin >> costs[i];

	cout << bruteforce(0) << endl;

	return 0;
}