#include <fstream>
#include <deque>

using namespace std;

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



const int N = 5000000;

int v[N];



int main()

{

    deque <int> dq;

    int n, k;

    long long suma = 0;

    cin >> n >> k;

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

    {

        cin >> v[i];

        if (!dq.empty() && dq.front() == i - k)
        {
            dq.pop_front();
        }
        while (!dq.empty() && v[i] <= v[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if (i >= k - 1)
        {
            suma += v[dq.front()];
        }

    }

    cout << suma;
    in.close();
    out.close();

    return 0;

}