#include <fstream>

using namespace std;

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

int dq[5000001], a[5000001], n, k, st, dr;
long long sum;

int main()
{
  fin >> n >> k;
  for (int i = 1; i <= n; i++)
    fin >> a[i];
  st = 1; dr = 0;
  for (int i = 1; i <= n; i++) {
    while (st <= dr and a[i] <= a[dq[dr]]) dr--;
    dr++;
    dq[dr] = i;
    if (dq[st] == i - k)
      st++;
    if (i >= k)
      sum += a[dq[st]];
  }
  fout << sum;
  return 0;
}