#include <fstream>
#include <stack>

using namespace std;

const int NMAX = 5000001;
int v[NMAX];

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n, k;
    fin >> n >> k;
    for (int i = 0; i < n; ++i)
        fin >> v[i];
    deque<int> dq;
    long long s = 0;
    for (int i = 0; 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 - 1)
            s += v[dq.front()];
    }
    fout << s;
    fin.close();
    fout.close();
    return 0;
}