#include<fstream>
using namespace std;
long v[5000001],d[5000001];
long long s=0;
ifstream f("deque.in");ofstream g("deque.out");
int main()
{
	long p=1,u=0,i,n,k;
 f>>n>>k;
 for(i=1;i<=n;i++)f>>v[i];
 for(i=1;i<=n;i++)
 {
	 while(p<=u && v[i]<=v[d[u]])
		 u--;
	 d[++u]=i;
	 if(d[p]+k<=i)
		 ++p;
	 if(i==k)
		 s+=v[d[p]];
 }
 g<<s;;return 0;
}