#include <fstream>
#include <vector>
#include <deque>

using namespace std;

int main() {
    ifstream in("deque.in");
    ofstream out("deque.out");

    int N, K;
    in >> N >> K;
    vector<long long> A(N);
    for (int i = 0; i < N; ++i) {
        in >> A[i];
    }

    deque<int> dq;
    long long sum = 0;

    for (int i = 0; i < N; ++i) {
        while (!dq.empty() && A[dq.back()] >= A[i]) {
            dq.pop_back();
        }
        dq.push_back(i);

        if (dq.front() <= i - K) {
            dq.pop_front();
        }

        if (i >= K - 1) {
            sum += A[dq.front()];
        }
    }

    out << sum << '\n';

    in.close();
    out.close();

    return 0;
}