#include<fstream>
using namespace std;

int v[5000001],d[5000001],i,n,k,p,u;
long long s;

int main()
{
	ifstream f("deque.in");
	ofstream g("deque.out");
	f >> n >> k;
	for (i=1;i<=n;i++)
		f >> v[i];
	p=1;u=0;s=0;
	for (i=1;i<=n;i++)
	{
		while ((p<=u) && (v[i]<=v[d[u]]))
			u--;
		u++;
		d[u]=i;
		if (i-d[p]==k)
			p++;
		if (i>=k)
			s+=v[d[p]];
	}
	g << s;
}