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

using namespace std;

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

int main() {
    int n, k;
    fin >> n >> k;
    deque<int> dq;
    vector<int> x(n);
    long long rezultat = 0;

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

        while (!dq.empty() && x[dq.back()] >= x[i]) {
            dq.pop_back();
        }
        while (!dq.empty() && dq.front() < i - k + 1) {
            dq.pop_front();
        }
        dq.push_back(i);

        if (i >= k - 1) {
            rezultat += x[dq.front()];
        }
    }

    fout << rezultat << endl;

    return 0;
}