#include <fstream>
#include <deque>

using namespace std;

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

const int N = 5000000;
int n, k;
long long v[N];
deque <int> dq;

int main()
{
    long long sum = 0;
    in >> n >> k;
    for (int i = 0; i < n; i++)
    {
        in >> 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()];
        }
    }
    out << sum;
    return 0;
}