#define _CRT_SECURE_NO_WARNINGS
#pragma comment(linker, "/stack:16777216")
#include <string>
#include <vector>
#include <map>
#include <list>
#include <iterator>
#include <set>
#include <queue>
#include <iostream>
#include <sstream>
#include <stack>
#include <deque>
#include <cmath>
#include <memory.h>
#include <cstdlib>
#include <cstdio>
#include <cctype>
#include <algorithm>
#include <utility>
#include <assert.h>
#include <time.h>


#include <fstream>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdio.h>
using namespace std;

#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, b, a) for(int i=(b)-1;i>=(a);--i)
#define FILL(A,value) memset(A,value,sizeof(A))
#define ALL(V) V.begin(), V.end()
#define SZ(V) (int)V.size()
#define PB push_back
#define MP make_pair
#define Pi 3.14159265358979

typedef long long Int;
typedef unsigned long long UInt;
typedef vector<int> VI;
typedef pair<int, int> PII;

const int INF = 1000000000;
const int MAX = 100007;
const int MAX2 = 1000000;
const int MAXD = 20;
const int BASE = 1000000007;
const int MOD = 1000000007;

int n , k;
int a[MAX];

int main() {

	//freopen("in.txt" , "r" , stdin);

	cin >> n >> k;
	FOR(i,0,n)
	{
		cin >> a[i];
	}
	Int res = 1LL * INF * INF;
	k = min(k , n);
	FOR(i,0,k + 1)
	{
		int j;
		Int cur = 0;
		for(j = i; j < n; j += 2 * k + 1)
		{
			cur += a[j];
		}
		j -= 2 * k + 1;
		if (n - 1 - j <= k)
		{
			res = min(res , cur);
		}
	}

	cout << res << endl;



    return 0;
}