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

int n, k, a[10005], i, j, rmq[20][10005], lg[10005];
long long ans = 1e18;

int main() {
    ios_base::sync_with_stdio(0);
    
    cin >> n >> k;
    for(i = 1; i <= n; ++i) cin >> a[i], rmq[0][i] = a[i];
  /*  for(i = 2; i <= n; ++i) lg[i] = lg[i / 2] + 1;
    
    for(i = 1; i <= n; ++i)
       for(j = 1; j - 1 + (1 << j) <= n; ++j)
            rmq[i][j] = min(rmq[i - 1][j], rmq[i - 1][j + 1 - (1 << (i - 1))]);
    */
    if(!k) {
        long long sum = 0;
        for(i = 1; i <= n; ++i) sum += a[i];
        return cout << sum << '\n', 0;
    }

    for(i = 1; i <= k + 1 && i <= n; ++i) {
        long long now = 0;
        for(j = i; j <= n; j += 2 * k + 1) now += a[j];
        
        ans = min(ans, now);
    }
    
    cout << ans << '\n';
    
    return 0;
}