#include <fstream>

using namespace std;

int a[5000002], poz[5000002], n, k;

int main()
{
    int i, pr, ul, x;
    long long suma;

    ifstream fin("deque.in");
    fin >> n >> k;
    pr = 0; ul = -1;
    for (i = 1; i <= k; ++i)
    {
        fin >> x;
        while (pr <= ul && x < a[ul]) ul--;
        a[++ul] = x;
        poz[ul] = i;
    }
    suma = a[pr];
    //cout << a[pr] << " " << poz[pr] << "\n";

    for (i = k + 1; i <= n; ++i)
    {
        fin >> x;
        while (pr <= ul && x < a[ul]) ul--;
        a[++ul] = x;
        poz[ul] = i;
        while (poz[ul] - k >= poz[pr]) ++pr;
        suma += a[pr];
        //cout << a[pr] << " " << poz[pr] << "\n";
    }
    fin.close();

    ofstream fout("deque.out");
    fout << suma << "\n";
    fout.close();

    return 0;
}