#include <fstream>
#include <queue>

using namespace std;

priority_queue <pair <int, int> , vector <pair <int, int> >, greater <pair <int, int> > > pq;

int main()
{
  ifstream in("deque.in");
  ofstream out("deque.out");

  int n, k, x;
  long long int suma = 0;

  in >> n >> k;
  for (int i = 1; i < k; i++)
  {
    in >> x;
    pq.push(make_pair(x, i));
  }
  for (int i = k; i <= n; i++)
  {
    in >> x;
    pq.push(make_pair(x, i));
    while (pq.top().second <= i - k)
    {
      pq.pop();
    }
    suma += pq.top().first;
  }

  out << suma;

  return 0;
}