#include<fstream>
using namespace std;

int a[5000001],b[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 >> a[i];
	p=1;
	for (i=1;i<=n;i++)
	{
		while ((u!=0) && (b[u]>=a[i]))
			u--;
		b[++u]=a[i];
		if ((i>k) && (b[p]==a[i-k]))
			p++;
		if (i>=k)
			s+=b[p];
	}
	g << s;
}