#include<fstream>
using namespace std;
int v[5000000],dq[5000000],st=1,dr,k;


ifstream in("deque.in");
ofstream out("deque.out");


void dreapta(int i)
{
	while((st<=dr)&&(v[dq[dr]]>=v[i]))
	{
		--dr;
	}
}



inline void stanga(int i)
{
	if(i-dq[st]==k)
		++st;
}




int main()
{
	int n,i;
	long long s=0;
	in>>n>>k;
	for(i=1;i<=n;++i)
		in>>v[i];
	for(i=1;i<=k;++i)
	{
		dreapta(i);
		dq[++dr]=i;
	}
	s=s+v[dq[st]];
	for(;i<=n;++i)
	{
		stanga(i);
		dreapta(i);
		dq[++dr]=i;
		s=s+v[dq[st]];
	}
	out<<s;
	return 0;
}