#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <string>
#include <string.h>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <assert.h>
#include <algorithm>
#include <iomanip>
#include <time.h>
#include <math.h>
#include <bitset>

#pragma comment(linker, "/STACK:256000000")

using namespace std;

typedef long long int int64;
typedef long double double80;

const int INF = (1 << 29) + 5;
const int64 LLINF = (1ll << 59) + 5;
const int MOD = 1000 * 1000 * 1000 + 7;

int n, k;
int64 arr[11111];

int main()
{
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);

	scanf("%d%d", &n, &k);

	for (int i = 0; i < n; ++i)
		scanf("%lld", &arr[i]);

	int64 answer = LLINF;
	int last = 0;

	int64 canswer;
	for (int i = 0; i <= k && i < n; ++i)
	{
		canswer = arr[i];
		last = i + k;
		for (int j = i + 2 * k + 1; j < n; j += 2 * k + 1)
		{
			//cout << i << " " << j << endl;
			canswer += arr[j];
			last = j + k;
		}
		//cout << i << " " << last << " " << canswer << endl;
		if (last >= n - 1)
		{
			answer = min(answer, canswer);
			//cout << "KEK" << endl;
		}
	}

	cout << answer;

	fclose(stdin);
	fclose(stdout);

	return 0;
}