#include <fstream>
#include <deque>
#include <algorithm>

using namespace std;

ifstream fin ("lapte.in");
ofstream fout ("lapte.out");

deque <int> v;

int n, k, s;

int main () {
    fin >> n >> k;
    int x;
    for (int i = 1; i <= n; i++) {
        fin >> x;
        v.push_back (x);
        if (i >= k) {
            int Min = 20000000;
            for (int i = 0; i <= k - 1; i++)
                Min = min (Min, v[i]);
            s += Min;
            v.pop_front ();
        }
    }

    fout << s;

    return 0;
}