#include <fstream>
#include <deque>

using namespace std;

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

const int DIM = 5000001;
int n, k;
int v[DIM];
deque<int> myDeque;

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

    long long sum = 0;
    for (int i = 1; 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;
}