#include<fstream>

using namespace std;

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

int st,dr,v[5000001],k,d[5000001]; 

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