#include <fstream>
#include <deque>

using namespace std;

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

int n, k, currentNr, sum;
deque<pair<int, int>> deq;

int main()
{
    fin >> n >> k;
    for (int i = 0; i < n; ++i) {
        fin >> currentNr;
        while (!deq.empty() && currentNr < deq.back().first) {
            deq.pop_back();
        }
        deq.push_back(make_pair(currentNr, i));
        if (i - deq.front().second == k) {
            deq.pop_front();
        }
        if (i >= k - 1)
            sum += deq.front().first;
    }
    fout << sum << "\n";
    return 0;
}