/*
https://infoarena.ro/problema/deque
*/
#include <fstream>
#include <deque>

using namespace std;

const int N = 5e6;

int x[N];

int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n, k;
    in >> n >> k;
    for (int i = 0; i < n; i++)
    {
        in >> x[i];
    }
    deque <int> dq;
    long long s = 0;
    for (int i = 0; i < n; i++)
    {
        while (!dq.empty() && x[i] <= x[dq.back()])
        {
            dq.pop_back();
        }
        if (!dq.empty() && dq.front() == i - k)
        {
            dq.pop_front();
        }
        dq.push_back(i);
        if (i >= k - 1)
        {
            s += x[dq.front()];
        }
    }
    out << s << "\n";
    in.close();
    out.close();
    return 0;
}