#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

int main()
{
	int n, k;
    fin >> n >> k;

    deque<int> dq;
    long long rezultat = 0; 

    for (int i = 0; i < n; i++) {
        int x;
        fin >> x;
        dq.push_back(x);

        if (dq.size() == k) {
            int elementmin = dq.front();
            for (int j = 1; j < dq.size(); j++) {
                elementmin = min(elementmin, dq[j]);
            }
            rezultat += elementmin;
            dq.pop_front();
        }
    }

    cout << rezultat << endl;

    return 0;

}