#include <fstream>
#include <vector>
#include <deque>

using namespace std;

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