#include <iostream>
#include <fstream>
#include <deque>

using namespace std;
deque<pair<long long, int>> q;

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

    long long N, K, x, sum = 0;
    fin >> N >> K;

    for (int i = 1; i <= N; ++i) {
        fin >> x;
        while (q.size() && x <= q.back().first) {
            q.pop_back();
        }
        q.push_back({x, i});
        while (q.front().second <= i - K) {
            q.pop_front();
        }
        if (i >= K) {
            sum += q.front().first;
        }
    }
    fout << sum;
    return 0;
}