#include <fstream>
#include <deque>
#include <vector>

using namespace std;

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

int main()
{
    int n, k;
    cin >> n >> k;
    long long sum = 0;
    vector <int> v(n);
    deque <int> dq;
    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)
            sum += v[dq.front()];
    }
    cout << sum;
    return 0;
}