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

using namespace std;

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

int main() {
    int n, k;
    fin >> n >> k;
    deque<int> dq;
    int64_t ans = 0;
    for (int i = 0; i < n; ++i) {
        int x;
        fin >> x;
        while (!dq.empty() && dq.back() >= x) {
            dq.pop_back();
        }
        dq.push_back(x);
        if (!dq.empty() && dq.front() <= x) {
            while (!dq.empty() && dq.front() <= i - k + 1) {
                dq.pop_front();
            }
        }
        if (i >= k - 1) {
            ans += dq.front();
        }
    }
    fout << ans;
    return 0;
}