#include <fstream>
using namespace std;

int *Deque,*A;
int n,k;
int head,tail;
long long sum;


int main()
{
    ofstream fout("deque.out");
    ifstream fin("deque.in");
    fin>>n>>k;
    Deque = new int[n+10];
    A = new int[n+10];
    for(int i=1;i<=n;i++) {fin>>A[i];Deque[i]=0;}
    head=1;tail=0;
    for(int i=1;i<=n;i++)
    {
        while(head<=tail && A[i]<=A[Deque[tail]])tail-=1;
	Deque[++tail]=i
        if(Deque[head]==i-k)head+=1;
        if(i>=k)sum+=A[Deque[head]];
    }
    fout<<sum;
    fin.close();
    fout.close();
    return 0;
}