#include <fstream>
#include <deque>

using namespace std;

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

int n, k;
long long sum;
deque<pair<long long, long long>> subseq;

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

        if (subseq.size() && subseq.front().second < i - k + 1)
            subseq.pop_front();

        while(subseq.size() && subseq.back().first > nr)
            subseq.pop_back();

        subseq.push_back(make_pair(nr, i));
        if (i >= k)
            sum += subseq.front().first;
    }
    fout << sum;
    return 0;
}