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

using namespace std;


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

    int suma=0, n, k, curent;
    deque<pair<int, int>> minim;

    fin >> n >> k;

    for (int i = 0; i < n; i++) {
        fin >> curent;
        while (!minim.empty() && minim.back().first > curent) minim.pop_back();
        minim.push_back({ curent,i });
        if (minim.front().second == i - k) minim.pop_front();
        if (i >= k - 1) suma += minim.front().first;
    }
    fout << suma;
    fin.close();
    fout.close();
}