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

ifstream cin("deque.in");
ofstream cout("deque.out");

#define N_MAX 5000005

int64_t a[N_MAX], n, k;
deque<int> deq;

int main() {
    cin >> n >> k;

    for (int i = 1; i <= n; ++i)
        cin >> a[i];

    int64_t suma = 0;
    for (int i = 1; i <= n; ++i) {
        while (!deq.empty() && a[i] <= a[deq.back()])
            deq.pop_back();

        deq.push_back(i);

        if (deq.front() == i - k)
            deq.pop_front();

        if (i >= k)
            suma += a[deq.front()];
    }

    cout << suma;
}