#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

typedef long long ll;

const ll Inf = 1000000000000000000ll;
const int Maxn = 10005;

int n, k;
int c[Maxn];
ll best = Inf;

int main() {
    scanf("%d %d", &n, &k);
    for (int i = 0; i < n; i++)
        scanf("%d", &c[i]);
    for (int i = 0; i < n && i <= k; i++) {
        ll cand = 0;
        for (int j = i; j < n; j += 2 * k + 1)
            cand += c[j];
        best = min(best, cand);
    }
    cout << best << endl;
    return 0;
}