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

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

struct DequeElement {
    int id;
    int val;
};

int n, k;
deque <DequeElement> d;

int main() {
    fin >> n >> k;
    long long sum = 0;

    for (int i = 1; i <= n; i++) {
        int x;
        fin >> x;
        
        while (!d.empty() && x <= d.back().val) {
            d.pop_back();
        }

        d.push_back({i, x});

        if (d.front().id == i - k) {
            d.pop_front();
        }

        if (i >= k) {
            sum += d.front().val;
        }
    }
    fout << sum << '\n';

    return 0;
}