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

using namespace std;

int main()
{
	ifstream in("deque.in");
    ofstream out("deque.out");

    int n, k;
    in >> n >> k;

    vector <int> v(n);
    long long s = 0;
    deque <int> dq;
    for (int i = 0; i < n; i ++)
    {
        in >> 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)
        {
            s += v[dq.front()];
        }
    }

    out << s;

    in.close();
    out.close();
    
    return 0;
}