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

typedef long long ll;

int main() {
    int k,n;
    cin >> n >> k;
    vector<ll> v(n);
    ll sum = 0;
    ll mn = 1000000001;
    for(int i=0;i<n;i++) {
        cin >> v[i];
        sum += v[i];
        mn = min(mn,v[i]);
    }
    if(!k) {
        cout << sum << endl;
    } else {
        ll cost;
        ll ans = sum;
        for(int i=0;i<n && i<=k;i++) {
            cost = v[i];
            for(int j=i+2*k+1;j<n;j+=2*k+1) {
                cost += v[j];
            }
            ans = min(ans,cost);
        }
        cout << ans << endl;
    }
    return 0;
}