#include <fstream>
#include <deque>

using namespace std;

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

deque<int> dq;
int v[5000005];

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