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

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

int n, k;

int main() {


    fin >> n >> k;

    deque<int> dq;

    vector<int> min_list;

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

        dq.push_back(x);

        if (dq.size() > k) {
            dq.pop_front();
        }

        if (dq.size() == k) {
            int min_val = dq.front();
            for (auto it = dq.begin(); it != dq.end(); it++) {
                if (*it < min_val) {
                    min_val = *it;
                }
            }
            min_list.push_back(min_val);
        }
    }

    long long sum = 0;
    for (auto it = min_list.begin(); it != min_list.end(); it++) {
        sum += *it;
    }

    fout << sum << endl;

    fin.close();
    fout.close();

    return 0;
}