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

using namespace std;

ifstream citeste("deque.in");
ofstream scrie("deque.out");

int n, k, a, s;
deque <int> poz;
int v[50000001];

void citire ()
{
    citeste >> n >> k;
    int i=1;
    while (citeste >> a)
    {
        v[i] = a;
        i++;
    }
}

void rezolvare ()
{
    for (int indice_valoare=1; indice_valoare<=n; indice_valoare++)
    {
        while (poz.size() != 0 && v[indice_valoare] <= v[poz.back()])
            poz.pop_back();
        poz.push_back(indice_valoare);
        if (indice_valoare >= k)
        {
            s = s + v[poz.front()];
            if (poz.front() == (indice_valoare - k + 1))
                poz.pop_front();
        }
    }
}

int main()
{
    citire();
    rezolvare();
    scrie << s;
    return 0;
}