#include <iostream>
#include <fstream>

using namespace std;


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

    int suma = 0, n, k, curent, * minim = nullptr, * poz = nullptr, inceput = 0, final = 0;

    fin >> n >> k;
    minim = new int[n];
    poz = new int[n];

    for (int i = 0; i < n; i++) {
        fin >> curent;
        while (final > inceput && minim[final] > curent) --final;
        minim[final] = poz[final] = curent;
        final++;
        if (poz[inceput] == i - k) inceput++;
        if (i >= k - 1) suma += minim[inceput];
    }
    fout << suma;
    fin.close();
    fout.close();
}