#include<fstream>
using namespace std;
#define NMAX 5000005
ifstream f("deque.in");
ofstream g("deque.out");
int dq[NMAX],a[NMAX],n,k,x,y;
long long sum;
int main()
{
	f>>n>>k>>a[1];
	int u,p=u=1;dq[p]=a[1];
	for(int i=2;i<=k;++i)
	{
		f>>a[i];
		while(a[i]<dq[u]&& p<=u)u--;
		dq[++u]=a[i];
	}
	sum+=dq[p];
	for(int i=k+1;i<=n;++i)
	{
		y=a[i-k];
		f>>a[i];
		if(dq[p]==y)p++;
		if(p<=u){
			while(a[i]<dq[u]&& p<=u)u--;
			dq[++u]=a[i];
		}
		else {dq[p]=a[i];u=p;}
		sum+=dq[p];
	}
	
	g<<sum;
	return 0;
}