#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <utility>
#include <cstdlib>
#include <memory>
#include <queue>
#include <cassert>
#include <cmath>
#include <ctime>
#include <complex>
#include <bitset>
#include <fstream>
#include <unordered_map>
#include <unordered_set>
#include <numeric>

using namespace std;

#define ws ws_____________________
#define y1 y1_____________________
#define y0 y0_____________________
#define left left_________________
#define right right_______________
#define next next_________________
#define prev prev_________________
#define hash hash_________________

#define pb push_back
#define fst first
#define snd second
#define mp make_pair 
#define sz(C) ((int) (C).size())
#define forn(i, n) for (int i = 0; i < (int) n; ++i)
#define ford(i, n) for (int i = ((int) n) - 1; i >= 0; --i)
#define all(C) begin(C), end(C)

typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int uint;
typedef pair<int,int> pii;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
typedef vector<int> vi;
typedef vector<vector <int> > vvi;
typedef vector<pii> vii;
typedef long double ld;
typedef complex<double> cd;
typedef vector<cd> vcd;

#define FILE_NAME "a"

const int MAXN = 1e4 + 10;
const ll INF = 1e18;

int n, k;
ll dp[MAXN];
ll min_dp[MAXN];
int c[MAXN];

bool read() {
	if  (scanf("%d%d", &n, &k) < 2) {
		return false;
	}
	forn(i, n) {
		scanf("%d", &c[i]);
	}
	return true;
}

ll solve() {
	ll ans = INF;
	forn(it, 2) {
		for (int i = 0; i - k <= 0; ++i) {
			ll cur = 0;
			int j;
			for (j = i; j < n; j += 2 * k + 1) {
				cur += c[j];
			}
			if  (j + k >= n - 1) {
				ans = min(ans, cur);
			}
		}
		reverse(c, c + n);
	}
	return ans;
}

int main() {
#ifdef LOCAL
	freopen(FILE_NAME ".in", "r", stdin);
	// freopen(FILE_NAME ".out", "w", stdout);
#endif

	while (read()) {
		cout << solve() << '\n';
	}

#ifdef LOCAL
	cerr.precision(5);
	cerr << "Time: " << fixed << (double) clock() / CLOCKS_PER_SEC << endl;
#endif
	return 0;
}