#include <fstream>
#include <cstring>
#include <algorithm>
#include <deque>
using namespace std;

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

const int MAXN = 5000005;
int n, m;
deque<pair<int, int>> q;

int main() {

    long long sol = 0;
    fin >> n >> m;

    for (int i = 1; i <= n; ++i) {
        int k;
        fin >> k;
        while (!q.empty() && k < q.back().first) {
            q.pop_back();
        }
        if (i >= m) {
            while (!q.empty() && q.front().second <= i - m) {
                q.pop_front();
            }
        }
        q.push_back({k, i});

        if (i >= m) {
            sol += (long long)q.front().first;
        }
    }

    fout << sol;

    fout.close();
    return 0;
}