#include<fstream>
#define NMAX 5000010
using namespace std;
int V[NMAX],Deque[NMAX],P,U,N,K;
long long S;
int main()
{ ifstream f("deque.in");
  ofstream g("deque.out");
  int i;
  f>>N>>K;
  for(i=1;i<=N;i++) f>>V[i];
  P=1,U=0;
  for(i=1;i<=N;i++)
  { while ((P<=U) && (V[i]<=V[Deque[U]])) U--;
  Deque[++U]=i;
  if(Deque[P]==i-K) P++;
  if(i>=K) S+=V[Deque[P]];
}
g<<S;
return 0;
}