#include <fstream>
#include <deque>

using namespace std;

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

int N, K;
int V[5000010];
deque<int> DQ;
long long sum;

int main()
{
    fin >> N >> K;

    for (int i = 1; i <= N; ++i)
        fin >> V[i];

    for (int i = 1; i <= N; ++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)
            sum += V[DQ.front()];
    }

    fout << sum << '\n';

    fin.close();
    fout.close();
    return 0;
}