#include <fstream>
#include <deque>

using namespace std;

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

int N, K;
long long sum;
int A[5000002];
deque<int> D;

int main()
{
    fin >> N >> K;
    for (int i = 1; i <= N; ++i)
        fin >> A[i];

    for (int i = 1; i <= N; ++i)
    {
        while (!D.empty() && A[i] <= A[D.back()])
            D.pop_back();
        D.push_back(i);
        if (D.front() == i - K)
            D.pop_front();
        if (i >= K)
            sum += A[D.front()];
    }

    fout << sum;

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