#include <fstream>

#define mxm 5000005

using namespace std;

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

int n, k, a[mxm], coada[mxm], i, jos=0, sus=1,
unsigned long long suma=0;

int main()
{
    fin >> n >> k;

    for (i=1; i<=n; i++)
        {
            fin >> a[i];
            while (sus <= jos && a[i] <= a[coada[jos]])
                jos--;
                jos++;
                coada[jos] = i;

            if (coada[sus] == i-k)
                sus++;
            if (i >= k)
                suma = suma + a[coada[sus]];
        }

    fout << suma;

    fin.close ();
    fout.close ();

    return 0;
}