#include <fstream>

using namespace std;

int MAX_N = 50001;

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    long a[MAX_N],deque[MAX_N],n,i,k,x,sum=0;
    int front=1,back=0;
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>a[i];
    for(i=1;i<=n;i++)
            {
              while(front<=back && a[i]<=a[deque[back]]) back--;
                deque[++back]=i;
              if(deque[front]==i-k) front++;
              if(i>=k)  sum+=a[deque[front]];
            }
    fout<<sum;
    fin.close();
    fout.close();
    return 0;
}