#include <fstream>
#include <deque>

using namespace std;

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

struct element {
    int pozitie;
    int valoare;
};
deque<element> dq;

int main()
{
    int n, k;
    cin >> n >> k;
    element x;
    long long suma=0;
    for (int i=1; i<=n; i++) {
        cin >> x.valoare;
        x.pozitie=i;
        while (dq.size()>=1) {
            if (x.valoare<=dq.back().valoare) dq.pop_back();
            else if (x.valoare>dq.back().valoare) break;
        }
        if (dq.size()>=1 && dq.front().pozitie==i-k) {
            dq.pop_front();
        }
        dq.push_back(x);
        if (i>=k) suma=suma+dq.front().valoare;
    }
    cout << suma;
    return 0;
}