#include<fstream>

using namespace std;

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

const int N = 5000001;

int v[N],d[N],dr=0,st=1,k;

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

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

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