/*
*/

#pragma comment(linker, "/STACK:16777216")
#define _CRT_SECURE_NO_WARNINGS

#include <fstream>
#include <iostream>
#include <string>
#include <complex>
#include <math.h>
#include <set>
#include <vector>
#include <map>
#include <queue>
#include <stdio.h>
#include <stack>
#include <algorithm>
#include <list>
#include <ctime>
#include <memory.h>
#include <assert.h>

#define y0 sdkfaslhagaklsldk
#define y1 aasdfasdfasdf
#define yn askfhwqriuperikldjk
#define j1 assdgsdgasghsf
#define tm sdfjahlfasfh
#define lr asgasgash
#define norm asdfasdgasdgsd

#define eps 1e-9
#define M_PI 3.141592653589793
#define bs 1000000007
#define bsize 350

using namespace std;

const int INF = 1e9;
const int N = 200031;

int n, k, ar[N];

long long solve(int start)
{
	long long res = 0;
	for (int i = start; i <= n; i += 2 * k + 1)
	{
		res += ar[i];
		if (i + k + 1 <= n&&i + k * 2 + 1 > n)
			return 1e18;
	}
	return res;
}

bool good_mask(int mask)
{
	int ar[25];

	for (int i = 0; i < n; i++)
	{
		ar[i] = 1;
	}
	for (int i = 0; i < n; i++)
	{
		if (mask&(1 << i))
		{
			for (int j = i - k; j <= i + k; j++)
			{
				if (j >= 0 && j < n)
					ar[j] ^= 1;
			}
		}
	}
	for (int i = 0; i < n; i++)
	{
		if (ar[i])
			return 0;
	}
	return 1;
}

int ans_mask;

int main(){
	//freopen("fabro.in","r",stdin);
	//freopen("fabro.out","w",stdout);
	//freopen("F:/in.txt", "r", stdin);
	//freopen("F:/output.txt", "w", stdout);
	ios_base::sync_with_stdio(0);
	//cin.tie(0);

	while (true)
	{
		cin >> n >> k;
		for (int i = 1; i <= n; i++)
		{
			cin >> ar[i];
			//ar[i] = rand() % 10;
		}

		long long ans = 1e18;

		/*for (int mask = 0; mask < (1 << n); mask++)
		{
		if (good_mask(mask))
		{
		int here = 0;
		for (int i = 0; i < n; i++)
		{
		if (mask&(1 << i))
		here += ar[i + 1];
		}
		if (here < ans)
		ans = min(ans, 0ll + here),
		ans_mask = mask;
		}
		}*/
		long long ans2 = 1e18;

		for (int F = 1; F <= k + 1&&F<=n; F++)
		{
			ans2 = min(ans2, solve(F));
		}

		/*if (ans != ans2)
		{
		cout << "!" << endl;
		for (int i = 1; i <= n; i++)
		{
		cout << ar[i] << " ";
		}
		cout << endl;
		cout << ans << " " << ans2 << " " << ans_mask << endl;
		while (true);
		}

		else
		cout << "OK" << endl;*/

		cout << ans2 << endl;
		return 0;
	}
	cin.get(); cin.get();
	return 0;
}