#include <fstream>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");

int a[5000000];
int dq[5000000];

int main() {

    int n, k;
    long long s = 0;
    int ic = 0, sf = -1;
    cin >> n >> k;

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

    for (int i = 0; i < n; ++i) {
        if (ic <= sf && dq[ic] < i - k + 1) {
            ic++;
        }

        while (ic <= sf && a[dq[sf]] > a[i]) {
            sf--;
        }

        dq[++sf] = i;

        if (i >= k - 1) {
            s += a[dq[ic]];
        }
    }

    cout << s ;
    return 0;
}