#include <iostream>
#include <fstream>

using namespace std;
int v[5000001], Deque[5000001], st, dr, N, K;
ifstream f ("deque.in");
ofstream g ("deque.out");
long long S;
int main()
{

  int i;
  f>>N>>K;
  for(i=1;i<=N;i++)
    f>>v[i];
  st=1;
  dr=0;
  for(i=1;i<=N;i++)
  {
      while((st<=dr)&&(v[i]<=v[Deque[dr]]))
      dr--;
      Deque[++dr]=i;
      if(Deque[st]==i-K)
      st++;
      if(i>=K) S+=v[Deque[st]];
  }
  g<<S;
  return 0;
}