#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; }