#include <fstream>
#include <deque>

#define DIM 5000001

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

int v[DIM];
std::deque<int> myDeque;

int main()
{
    int n, k;
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
        fin >> v[i];

    long long sum = 0;
    myDeque.push_back(1);
    for (int i = 2; i <= n; i++)
    {
        while (!myDeque.empty() && v[i] < v[myDeque.back()])
            myDeque.pop_back();
        myDeque.push_back(i);

        if (i - myDeque.front() == k)
            myDeque.pop_front();
        if (i >= k)
            sum += v[myDeque.front()];
    }

    fout << sum;

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