#include<fstream>

using namespace std;

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

int n,k,v[5000000],d[5000000],st,dr;

void stanga(int i)
{
	if(i-k==d[st])
		++st;
}
void dreapta(int i)
{
	while(st<=dr && v[d[dr]]>=v[i])
		--dr;
}

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