#include <fstream>
#include <deque>

using namespace std;

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

const int N = 5000000;
int v[N];

int main()

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

}