#include <stdio.h>
#include <bits/stdc++.h>
using namespace std;
 

#define REP(i,n) for(int(i)=0;(i)<(int)(n);(i)++)

#include <vector>
#include <utility>


#include <algorithm>


int n, k;
int c[11000];
long long pd[11000];

void solve() {
	scanf("%d %d", &n, &k);
	REP(i,n) scanf("%d", &c[i]);

	long long ans = 1000000000000000000LL;
	for (int st = 0; st <= k && st < n; st++) {
		int la = 0;
		long long co = 0;
		for (int i = st; i < n; i += 2*k+1) {
			co += c[i];
			la = i;
		}

		if (n-la <= k+1) ans = min(ans, co);
	}

	printf("%lld\n", ans);
}


int main() {
    solve();
}