#include <iostream>
#include <fstream>

#define NMAX 5000010

using namespace std;

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

int v[NMAX], dq[NMAX];

int main()
{
    int n, k;
    int st = 0, dr = 1;
    long long rez = 0;

    fin >> n >> k;

    for (int i = 1; i <= n; fin >> v[i++]);

    for (int i = 1; i <= n; i++)
    {
        while (dr <= st && v[i] <= v[dq[st]]) --st;

        dq[++st] = i;
        if (dq[dr] == i - k) ++dr;
        if (i >= k) rez += v[dq[dr]];
    }

    fout << rez;

    return 0;
}