#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

int main()
{
    int n, k, x;
    deque<int> dq;
    long long sum = 0;

    in >> n >> k;

    for (int i = 1; i <= n; i++)
    {
        in >> x;

        if (!dq.empty() && dq.front() == i - k)
        {
            dq.pop_front();
        }

        while (!dq.empty() && x < dq.back())
        {
            dq.pop_back();
        }

        dq.push_back(x);

        if (i >= k)
        {
            sum += dq.front();
        }
    }

    out << sum << endl;

    in.close();
    out.close();

    return 0;
}