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

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int main() {
    int n, k;
    f>> n >> k;

    vector<int> a(n);
    deque<int> dq;
    long long sum = 0;

    for (int i = 0; i < n; i++) {
        f>> a[i];

        // stergem elem care sunt >= a[i]
        while (!dq.empty() && a[dq.back()] >= a[i]) {
            dq.pop_back();
        }

        // stergem elem care nu mai sunt variabile
        while (!dq.empty() && dq.front() < i - k + 1) {
            dq.pop_front();
        }

        // punem i in dq
        dq.push_back(i);

        // calc. suma
        if (i >= k - 1) {
            sum += a[dq.front()];
        }
    }

    g<< sum << endl;

    return 0;
}