#include <fstream>
#include <deque>

using namespace std;

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

const int max_size = 5e6 + 1;

int v[max_size];
deque <int> dq;

int main ()
{
    int n, k;
    in >> n >> k;
    for (int i = 1; i < k; i++)
    {
        in >> v[i];
        while (!dq.empty() && v[i] <= v[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);
    }
    long long ans = 0;
    for (int i = k; i <= n; i++)
    {
        in >> v[i];
        if (dq.front() == i - k)
        {
            dq.pop_front();
        }
        while (!dq.empty() && v[i] <= v[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        ans += 1LL * v[dq.front()];
    }
    out << ans;
    in.close();
    out.close();
    return 0;
}