#include <fstream>
#include <deque>
#define nmax 5000002
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int a[nmax],i,n,k,sum;

void citire ()
{
  f>>n>>k;
  for (i=1; i<=n; i++)
    f>>a[i];
  f.close ();
}

void solve ()
{
  deque <int> q;
  
  for (i=1; i<=n; i++)
  {
    while (!q.empty() && a[i]<=a[q.back()]) q.pop_back();
    q.push_back (i);
    if (q.front ()==i-k)
      q.pop_front ();
    if (i>=k) sum+=a[q.front()];
  }
}

void afisare ()
{
  g<<sum;
  g.close ();
}

int main ()
{
  citire ();
  solve ();
  afisare ();
  return 0;
}