#include <iostream>
#include <fstream>
#include <queue>

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

int n, k;
std::deque<std::pair<int, int>> dq;

int main() {
    int number;
    long long sum(0);
    fin >> n >> k;
    for (int i = 1; i <= n; i++) {
        fin >> number;
        while (!dq.empty() && dq.front().first <= i - k)
            dq.pop_front();
        while (!dq.empty() && dq.back().second >= number)
            dq.pop_back();
        dq.push_back(std::make_pair(i, number));
        if (i >= k) sum += dq.front().second;
    }

    fout << sum << "\n";
}