#include <iostream>
#include <fstream>

using namespace std;

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

long n, k, v[50000000], poz[5000000], st = 0, dr = -1, sum;

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

    for (int i = 0; i < n; i++)
    {

        in >> v[i];

        if (st <= dr && poz[st] == i - k) {
            st++;
        }

        while (st <= dr && v[i] <= v[poz[dr]]) {
            dr--;
        }

        poz[++dr] = i;

        if (i >= k - 1) {
            sum += v[poz[st]];
        }

    }

    out << sum;
    return 0;
}