#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,inceput,sfarsit,q[5000001],mi,i,x,j,a[5000001];
long long s;
int main()
{
   f>>n>>k;
   inceput=1;
   for(i=1;i<=n;i++)
    f>>a[i];
   for(i=1;i<=n;i++)
   {
       while(inceput<=sfarsit&&a[i]<=a[q[sfarsit]])
        sfarsit--;
     q[++sfarsit]=i;
   if(q[inceput]==i-k)
    inceput++;
    if (i>=k)
        s+=a[q[inceput]];
   }
   g<<s;
    return 0;
}