#include <bits/stdc++.h>
using namespace std;
#define sz(x) ((int) (x).size())
#define forn(i,n) for (int i = 0; i < int(n); ++i)
typedef long long ll;
typedef long long i64;
typedef long double ld;
const int inf = int(1e9) + int(1e5);
const ll infl = ll(2e18) + ll(1e10);

const int maxn = 10010;
int a[maxn];

int main() {
    #ifdef LOCAL
    assert(freopen("d.in", "r", stdin));
    #else
    #endif
    int n, k;
    cin >> n >> k;
    forn (i, n)
        cin >> a[i];
    ll res = infl;
    for (int st = 0; st < n && st <= k; ++st) {
        ll cur = a[st];
        int r = st + k;
        while (r + 1 < n) {
            int to = r + 1 + k;
            if (to >= n) {
                cur = infl;
                break;
            }
            cur += a[to];
            r = to + k;
        }
        res = min(res, cur);
    }
    cout << res << '\n';
}